Irreversible electroporation using tissue vasculature to treat aberrant cell masses or create tissue scaffolds

ABSTRACT

The present invention relates to the field of medical treatment of diseases and disorders, as well as the field of biomedical engineering. Embodiments of the invention relate to the delivery of Irreversible Electroporation (IRE) through the vasculature of organs to treat tumors embedded deep within the tissue or organ, or to decellularize organs to produce a scaffold from existing animal tissue with the existing vasculature intact. In particular, methods of administering non-thermal irreversible electroporation (IRE) in vivo are provided for the treatment of tumors located in vascularized tissues and organs. Embodiments of the invention further provide scaffolds and tissues from natural sources created using IRE ex vivo to remove cellular debris, maximize recellularization potential, and minimize foreign body immune response. The engineered tissues can be used in methods of treating subjects, such as those in need of tissue replacement or augmentation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a Divisional Application ofU.S. patent application Ser. No. 15/843,888, filed Dec. 15, 2017, whichpublished as U.S. Patent Application Publication No. 2018/0125565 on May10, 2018. The '888 application claims priority to and is a DivisionalApplication of U.S. patent application Ser. No. 13/989,175, filed May23, 2013, which published as U.S. Patent Application Publication No.2013/0253415 on Sep. 26, 2013, and issued as U.S. Pat. No. 9,867,652 onJan. 16, 2018. The '175 application is a National Stage Applicationunder 35 U.S.C. § 371 of International Application No. PCT/US11/62067,filed Nov. 23, 2011, which published as International Publication No. WO2012/071526 on May 31, 2012. The '067 application claims priority to andthe benefit of the filing date of U.S. Provisional Patent ApplicationNo. 61/416,534, filed Nov. 23, 2010 and claims priority to and is aContinuation-In-Part (CIP) application of U.S. patent application Ser.No. 12/491,151, filed Jun. 24, 2009, which published as U.S. PatentApplication Publication No. 2010/0030211 on Feb. 4, 2010, and whichissued as U.S. Pat. No. 8,992,517 on Mar. 31, 2015. The '151 applicationclaims priority to and the benefit of the filing date of U.S.Provisional Patent Application Nos. 61/075,216, filed Jun. 24, 2008;61/125,840, filed Apr. 29, 2008; 61/171,564, filed Apr. 22, 2009; and61/167,997, filed Apr. 9, 2009. The '067 application claims priority toand is a CIP application of U.S. patent application Ser. No. 12/432,295,filed Apr. 29, 2009, which published as U.S. Patent ApplicationPublication No. 2009/0269317 on Oct. 29, 2009, and issued as U.S. Pat.No. 9,598,691 on Mar. 21, 2017. The '295 application claims priority toand the benefit of the filing date of U.S. Provisional PatentApplication No. 61/125,840, filed Apr. 29, 2008. The entire disclosuresof all of these patent applications are hereby incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the field of medical treatment ofdiseases and disorders, as well as the field of biomedical engineering.Embodiments of the invention relate to the delivery of IrreversibleElectroporation (IRE) through the vasculature of organs to treat tumorsembedded deep within the tissue or organ, or to decellularize organs toproduce a scaffold from existing animal tissue, such as human tissue,with the existing vasculature intact. In addition, embodiments of theinvention may be used in the treatment of malignant and benign diseasesthrough the enhanced administration of therapeutic drugs or geneconstructs by facilitating reversible electroporation. Further, vascularelectrical conduits may be used to administer other therapies that relyon the delivery of electrical energy to a targeted region of the body ororgan tissue with the existing vasculature intact.

Description of Related Art

The ablation of unwanted soft tissue can be achieved by many means,including surgical excision, application of excessive amount of ionizingradiation or other forms of energy (excessive heating and cooling),exposure to cytotoxic chemicals, or by a combination of these means. Itis common to use these means to destroy neoplasms. Treatments known inthe art involve surgical intervention to physically remove the aberrantcell mass, radiation to kill the cells of the aberrant cell mass,exposure of aberrant cells to toxic chemicals (i.e., chemotherapy), or acombination of such techniques. While each treatment modality has shownsignificant effectiveness in treatment of various cell proliferativediseases, no one technique has been shown to be highly effective attreating all types of cell proliferative diseases and disorders.

While surgical intervention is effective at removal of solid tumors ontissues and organs that are physically accessible and capable ofsustaining physical damage or capable of regeneration, surgicalintervention can be difficult to perform on tumors that are not readilyaccessible or on organs that do not regenerate. In these cases, surgicalintervention can often involve substantial physical damage to thepatient, requiring extensive recuperation times and follow-ontreatments. At other times, the extensive growth of the neoplasmprevents removal, since attempts at removal would likely kill thepatient. Likewise, treatment with radiation can result in collateraldamage to tissue surrounding the tumor, and can cause long-lastingside-effects, which can lower the quality of life of the patient.Chemotherapeutic treatments can cause systemic damage to the patient,and can result in significant side effects that might require a longrecuperation period or cause permanent damage to tissues and organs.

Recent work by the inventors has focused on the ablation of unwantedsoft tissue (malignant tumors) by application of excessive electricalenergy, using a technique termed Irreversible Electroporation (IRE).Successful control and/or ablation of soft tissue sarcoma and malignantglioma have been achieved. Irreversible electroporation (IRE) involvesplacing electrodes within or near the targeted region to deliver aseries of low energy, microsecond electric pulses. These pulsespermanently destabilize the cell membranes of the targeted tissue (e.g.,tumor), thereby killing the cells. When applied with precision, IRE doesnot damage major blood vessels, does not require the use of drugs andnon-thermally kills neoplastic cells in a controllable manner, withoutsignificantly damaging surrounding tissue.

Other methods of treating disease involve replacing diseased tissue ororgans. Over the past twenty years, organ transplantation has become astandard care for patients diagnosed with end stage diseases likecirrhosis, renal failure, etc. The extraordinary success of livertransplantation, with 90% and 75% survival rates after 1 and 5 years,respectively, has led to a progressively increasing number of patientsawaiting transplant. Chan, S. C. et al., A decade of right liveradult-to-adult living donor liver transplantation—The recipient mid-termoutcomes. Annals of Surgery 248, 411-418,doi:10.1097/SLA.0b013e31818584e6 (2008) (“Chan 2008”).

According to the United Network of Organ Sharing (UNOS), there are over108,000 candidates in the US alone currently waiting for organtransplants including kidney, liver, heart, lung, and many others. Ofthose, there are over 16,000 candidates in immediate (one year) need ofa liver transplant, and at least 100,000 additional patients withadvanced liver disease who would benefit from one. In 2009, there werefewer than 7,000 liver transplants from both living and deceased donors.United Network of Organ Sharing, <http://www.unos.org> (2010).

Standard liver transplantation in the US is usually predicated on organremoval from the donor coincident with the onset of brainstem death. SeeKootstra, G., Daemen, J. H. C. & Oomen, A. P. A. Categories ofNon-Heart-Beating Donors, Transplant. Proc. 27, 2893-2894 (1995);Rigotti, P. et al. Non-Heart-beating Donors—An Alternative Organ Sourcein Kidney Transplantation, Transplant. Proc. 23, 2579-2580 (1991); andBalupuri, S. et al. The trouble with kidneys derived from the nonheart-beating donor: A single center 10-year experience. Transplantation69, 842-846 (2000).

Despite advances in transplant surgery and general medicine, the numberof patients awaiting transplant organs continues to grow, while thesupply of organs does not. The growing discrepancy between organ supplyand clinical demand is due to a number of factors including an increasein population age, an increasing incidence of diseases requiring livertransplants (hepatocellular carcinoma and infection with hepatitisviruses), rapid organ degradation (hours) after donation, mismatchescreated by histocompatibility and other immunologic phenomena, and sizemismatches between organs and potential recipients (including pediatricpatients), transplantation is the only workable treatment for patientssuffering end stage liver disease (Murray, K. F. & Carithers, R. L.AASLD practice guidelines: Evaluation of the patient for livertransplantation. Hepatology 41, 1407-1432, doi:10.1002/hep.20704(2005)); increased incidence of non-alcoholic fatty liver disease(Amarapurkar, D. N. et al. How common is non-alcoholic fatty liverdisease in the Asia-Pacific region and are there local differences? J.Gastroenterol. Hepatol. 22, 788-793,doi:10.1111/j.1440-1746.2007.05042.x (2007)); and acceptance oftransplantation for patients with metabolic or congenital diseases(Miro, J. M., Laguno, M., Moreno, A., Rimola, A. & Hosp Clin, O. L. T.H. I. V. W. G. Management of end stage liver disease (ESLD): What is thecurrent role of orthotopic liver transplantation (OLT)? J. Hepatol. 44,S140-S145, doi:10.1016/j.jhep.2005.11.028 (2006)).

Organ supply is constrained by obstacles that impede acquisition. Forexample, the requirement for organ removal coincident with brainstemdeath necessitates the use of hospital resources to maintain artificiallife support. As a result, organ donation may be problematic whenintensive care resources are strained. Fabre. Report of the BritishTransplantation Society Working Party on Organ Donation. (1995). Use oflife support for preservation of potential organ donations has beenethically debated (See Feest, T. G. et al., Protocol for IncreasingOrgan Donation After Cerebrovascular Deaths in a District GeneralHospital, Lancet 335, 1133-1135 (1990); and Riad, H. & Nicholls, A., AnEthical Debate Elective Ventilation of Potential Organ Donors, Br. Med.1 310, 714-715 (1995)), and donation refusal is common in regions wheresocial, cultural, and religious pressures place constraints on organprocurement.

The increasing gap between organ donation and supply to patients hascaused an increased interest in alternative organ sources. Perera, M.,Mirza, D. F. & Elias, E. Liver transplantation: Issues for the next 20years. J. Gastroenterol. Hepatol. 24, S124-S131,doi:10.1111/j.1440-1746.2009.06081.x (2009). Developing engineeredmaterials to replicate the structure and function of organs has been metwith limited success. Large volumes of poorly-organized cells andtissues cannot be implanted due to the initial limited diffusion ofoxygen, nutrients and waste. Folkman, J. Self-Regulation of Growth In 3Dimensions. Journal of Experimental Medicine 338 (1973); and Kaufman, D.S., Hanson, E. T., Lewis, R. L., Auerbach, R. & Thomson, J. A.Hematopoietic colony-forming cells derived from human embryonic stemcells. Proc. Natl. Acad. Sci. U S. A. 98, 10716-10721 (2001).

Despite this, researchers have made some progress toward partial organregeneration. For instance, mouse renal cells, grown on decellularizedcollagen matrices and implanted into athymic mice, developednephron-like structures after 8 weeks. Atala, A. Engineering organs.Curr. Opin. Biotechnol. 20, 575-592, doi:10.1016/j.copbio.2009.10.003(2009) (“Atala 2009”). In addition, five millimeter thick porouspolyvinyl-alcohol (PVA) constructs, implanted in mice and then injectedwith hepatocytes, developed liver-like morphology over the course of oneyear. Kaufmann, P. M. et al. Long-term hepatocyte transplantation usingthree-dimensional matrices. Transplant. Proc. 31, 1928-1929 (1999)(“Kaufmann 1999”). Cell survival and proliferation in each of thesestructures was limited to a few millimeters from a nutrient source.

For the development and differentiation of full organs suitable forhuman transplantation, structures that provide microvasculature neededfor the delivery of nutrients throughout the tissue and a physicalsemirigid matrix for cellular organization and anchorage must bedeveloped. See Atala 2009; Kaufmann 1999; and Atala, A. Experimental andclinical experience with tissue engineering techniques for urethralreconstruction. Urologic Clinics of North America 29, 485−+(2002).Traditional top-down manufacturing techniques are currently unable toproduce a hierarchical vascular structure which, in human organs, rangesin size from a several centimeters (vena cava, for example) down to onlya few micrometers (most capillaries), a scale spanning more than fourorders of magnitude. Microfabrication techniques can replicate somefeatures of the complex architecture of mammalian microvasculature, butcurrent processes fail to extend into the macro-scale. Structures whichhave features spanning multiple length scales are currently onlyfabricated through biological mechanisms and the relatively new field ofbiofabrication has developed, with the goal of utilizing andmanipulating these processes.

Bioengineered tissues have been fabricated through a number of schemes,including direct printing and biospraying, in which cells and asupporting matrix are simultaneously deposited to form a complexnetwork. See Mironov, V. et al. Organ printing: Tissue spheroids asbuilding blocks. Biomaterials 30, 2164-2174,doi:10.1016/j.biomaterials.2008.12.084 (2009); Nakamura, M. et al.Biocompatible inkjet printing technique for designed seeding ofindividual living cells. Tissue Engineering 11, 1658-1666 (2005); andCampbell, P. G. & Weiss, L. E. Tissue engineering with the aid of inkjetprinters. Expert Opin. Biol. Ther. 7, 1123-1127,doi:10.1517/14712598.7.8.1123 (2007). Centrifugal forces have beenemployed to create cross-linked hydrogels, with dense embedded cellularnetworks in tubular structures. Kasyanov, V. A. et al. Rapidbiofabrication of tubular tissue constructs by centrifugal casting in adecellularized natural scaffold with laser-machined micropores. J.Mater. Sci.-Mater. Med. 20, 329-337, doi:10.1007/s10856-008-3590-3(2009). Dielectrophoretic (Albrecht, D. R., Sah, R. L. & Bhatia, S. N.Geometric and material determinants of patterning efficiency bydielectrophoresis. Biophys. J. 87, 2131-2147,doi:10.1529/biophysj.104.039511 (2004)) and magnetic forces (Mironov,V., Kasyanov, V. & Markwald, R. R. Nanotechnology in vascular tissueengineering: from nanoscaffolding towards rapid vessel biofabrication.Trends Biotechnol. 26, 338-344, doi:10.1016/j.tibtech.2008.03.001(2008)) have been employed to guide the arrangement of cells withinsynthetic matrices and cells embedded in a bio-polymer have beenelectrospun into tissue constructs (Stankus, J. J., Guan, J. J.,Fujimoto, K. & Wagner, W. R. Microintegrating smooth muscle cells into abiodegradable, elastomeric fiber matrix. Biomaterials 27, 735-744,doi:10.1016/j.biomaterials.2005.06.020 (2006)). These techniques attemptto distribute cells within a suitable synthetically-fabricated network,leaving the embedded cells to reorganize into an optimal structure.

Decellularization of existing tissues extends the concept ofbiofabrication by taking advantage of the body's natural programming tocreate a complete tissue, including a functional vascular network. Ratliver extracellular matrix constructs have been created using chemicaldecellularization and reseeding. Baptista, P. M. et al. Generation of aThree-Dimensional Liver Bioscaffold with an Intact Vascular Network forWhole Organ Engineering (Wake Forest Institue for Regenerative MedicineHarvard-MIT Division of Health, Science, and Technology Rice University,2009). Decellularized rat hearts, reseeded with multiple cell types, cancontract and have the ability to generate pumping pressures. Ott, H. C.et al. Perfusion-decellularized matrix: using nature's platform toengineer a bioartificial heart. Nature Medicine 14, 213-221,doi:10.1038/nm1684 (2008). Challenges to chemical decellularizationtechniques include the potential for detergents to damage ECMcomponents, the potential to create and deposit toxins, and the inherentdifficulty of scaling these techniques up from small rat organs tolarger organs. These challenges must be overcome before decellularizedorgans can successfully be translated to the clinical setting.

Xenotransplantation, or the transplantation of animal organs, is onepotential solution to future organ shortages. Keeffe, E. B. Livertransplantation: Current status and novel approaches to liverreplacement. Gastroenterology 120, 749-762, doi:10.1053/gast.2001.22583(2001). Porcine xenotransplants have shown considerable potential, buthave failed to become widely accepted or used. Transplantation ofporcine pancreatic islets has recently been shown to temporarily reversediabetes mellitus (See Cardona, K. et al. Long-term survival of neonatalporcine islets in nonhuman primates by targeting costimulation pathways.Nature Medicine 12, 304-306, doi:10.1038/nm1375 (2006); and Hering, B.J. et al. Prolonged diabetes reversal after intraportalxenotransplantation of wild-type porcine islets in immunosuppressednonhuman primates. Nature Medicine 12, 301-303, doi:10.1038/nm1369(2006)) and the use of T-cell tolerance protocols have demonstrated thepotential for long-term kidney transplantation in non-human primates.Yamada, K. et al. Marked prolongation of porcine renal xenograftsurvival in baboons through the use of alpha 1,3-galactosyltransferasegene-knockout donors and the cotransplantation of vascularized thymictissue. Nature Medicine 11, 32-34, doi:10.1038/nm1172 (2005).

Additionally, porcine livers have demonstrated the ability to clearammonium and restore coagulation while under short term perfusion ofhuman plasma. Chari, R. S. et al. Brief Report—Treatment of HepaticFailure with ex-vivo Pig Liver Perfusion Followed by LiverTransplantation, N. Engl. J. Med. 331, 234-237 (1994); and Makowka, L.et al., The Use of a Pig Liver Zenograft for Temporary Support of aPatient with Fulminant Hepatic Failure, Transplantation 59, 1654-1659(1995). Unfortunately, the mechanisms of graft loss and rejection inthese transplants are still not well understood, and immunologicalrejection remains the most significant barrier to successfultransplantation. Yang, Y. G. & Sykes, M. Xenotransplantation: currentstatus and a perspective on the future. Nat. Rev. Immunol. 7, 519-531,doi:10.1038/nm2099 (2007).

Tissue engineering holds great promise for treating some of the mostdevastating diseases of our time. Because engineered tissue and organreplacements can be developed in a laboratory, therapies can potentiallybe delivered on a large scale, for multiple disease states with dramaticreduction in waiting times for patients. The concept of engineeringtissue using selective cell transplantation has been appliedexperimentally and clinically for a variety of disorders, including thesuccessful use of engineered bladder tissue for bladder reconstruction,engineered injectable chondrocytes for the treatment of vesicoureteralreflux and urinary incontinence, and vascular grafts. For clinical usefor humans, the process involves the in vitro seeding and attachment ofhuman cells onto a scaffold. Once seeded, the cells proliferate, migrateinto the scaffold, and differentiate into the appropriate cell type forthe specific tissue of interest while secreting the extracellular matrixcomponents required to create the tissue. The three dimensionalstructure of the scaffold, and in particular the size of pores anddensity of the scaffold, is important in successful proliferation andmigration of seeded cells to create the tissue of interest. Therefore,the choice of scaffold is crucial to enable the cells to behave in therequired manner to produce tissues and organs of the desired shape andsize.

To date, scaffolding for tissue engineering has usually consisted ofnatural and synthetic polymers. Methods known in the art for formingscaffolds for tissue engineering from polymers include solvent-casting,particulate-leaching, gas foaming of polymers, phase separation, andsolution casting. Electrospinning is another popular method for creatingscaffolds for engineered tissues and organs, but widely used techniquessuffer from fundamental manufacturing limitations that have, to date,prevented its clinical translation. These limitations result from thedistinct lack of processes capable of creating electrospun structures onthe nano-, micro-, and millimeter scales that adequately promote cellgrowth and function.

Of fundamental importance to the survival of most engineered tissuescaffolds is gas and nutrient exchange. In nature, this is accomplishedby virtue of microcirculation, which is the feeding of oxygen andnutrients to tissues and removing waste at the capillary level. However,gas exchange in most engineered tissue scaffolds is typicallyaccomplished passively by diffusion (generally over distances less than1 mm), or actively by elution of oxygen from specific types of materialfibers. Microcirculation is difficult to engineer, particularly becausethe cross-sectional dimension of a capillary is only about 5 to 10micrometers (μm; microns) in diameter. As yet, the manufacturingprocesses for engineering tissue scaffolds have not been developed andare not capable of creating a network of blood vessels. Currently, thereare no known tissue engineering scaffolds with a circulation designedinto the structure for gas exchange. As a result, the scaffolds fortissues and organs are limited in size and shape.

In addition to gas exchange, engineered tissue scaffolds must exhibitmechanical properties comparable to the native tissues that they areintended to replace. This is true because the cells that populate nativetissues sense physiologic strains, which can help to control tissuegrowth and function. Most natural hard tissues and soft tissues areelastic or viscoelastic and can, under normal operating conditions,reversibly recover the strains to which they are subjected. Accordingly,engineered tissue constructs possessing the same mechanical propertiesas the mature extracellular matrix of the native tissue are desirable atthe time of implantation into the host, especially load bearingstructures like bone, cartilage, or blood vessels.

There are numerous physical, chemical, and enzymatic ways known in theart for preparing scaffolds from natural tissues. Among the most commonphysical methods for preparing scaffolds are snap freezing, mechanicalforce (e.g., direct pressure), and mechanical agitation (e.g.,sonication). Among the most common chemical methods for preparingscaffolds are alkaline or base treatment, use of non-ionic, ionic, orzwitterionic detergents, use of hypo- or hypertonic solutions, and useof chelating agents. Common enzymatic methods for preparing scaffoldsinclude the use of trypsin, endonucleases, or exonucleases. Currently,it is recognized in the art that, to fully decellularize a tissue toproduce a scaffold, two or more of the above-noted ways, andspecifically two or more ways from different general classes (i.e.,physical, chemical, enzymatic), should be used. Unfortunately, themethods used must be relatively harsh on the tissue so that completeremoval of cellular material can be achieved. The harsh treatmentsinvariable degrade the resulting scaffold, destroying vasculature andneural structures.

The most successful scaffolds used in both pre-clinical animal studiesand in human clinical applications are biological (natural) and made bydecellularizing organs of large animals (e.g., pigs). In general,removal of cells from a tissue or an organ for preparation of a scaffoldshould leave the complex mixture of structural and functional proteinsthat constitute the extracellular matrix (ECM). The tissues from whichthe ECM is harvested, the species of origin, the decellularizationmethods and the methods of terminal sterilization for these biologicscaffolds vary widely. However, as mentioned above, thedecellularization methods are relatively harsh and result in significantdestruction or degradation of the extracellular scaffold. Once thescaffold is prepared, human cells are seeded so they can proliferate,migrate, and differentiate into the specific tissue. The intent of mostdecellularization processes is to minimize the disruption to theunderlying scaffold and thus retain native mechanical properties andbiologic properties of the tissue. However, to date this intent has notbeen achieved. Snap freezing has been used frequently fordecellularization of tendinous, ligamentous, and nerve tissue. Byrapidly freezing a tissue, intracellular ice crystals form that disruptcellular membranes and cause cell lysis. The rate of temperature changemust be carefully controlled to prevent the ice formation fromdisrupting the ECM as well. While freezing can be an effective method ofcell lysis, it must be followed by processes to remove the cellularmaterial from the tissue.

Cells can be lysed by applying direct pressure to tissue, but thismethod is only effective for tissues or organs that are notcharacterized by densely organized ECM (e.g., liver, lung). Mechanicalforce has also been used to delaminate layers of tissue from organs thatare characterized by natural planes of dissection, such as the smallintestine and the urinary bladder. These methods are effective, andcause minimal disruption to the three-dimensional architecture of theECM within these tissues. Furthermore, mechanical agitation andsonication have been utilized simultaneously with chemical treatment toassist in cell lysis and removal of cellular debris. Mechanicalagitation can be applied by using a magnetic stir plate, an orbitalshaker, or a low profile roller. There have been no studies performed todetermine the optimal magnitude or frequency of sonication fordisruption of cells, but a standard ultrasonic cleaner appears to beeffective. As noted above, currently used physical treatments aregenerally insufficient to achieve complete decellularization, and mustbe combined with a secondary treatment, typically a chemical treatment.Enzymatic treatments, such as trypsin, and chemical treatment, such asionic solutions and detergents, disrupt cell membranes and the bondsresponsible for intercellular and extracellular connections. Therefore,they are often used as a second step in decellularization, after grossdisruption by mechanical means.

Although advances have been made recently in the field of IRE and theconcept of treatment of tumors with IRE has been established, thepresent inventors have recognized that there still exists a need in theart for improved devices and methods for ablating diseased tissues usingIRE. More specifically, the inventors employ the vascular bed of tissuesas a physiologic electrode (“Physiologic Vascular Electrode” or “PVE”)to selectively ablate cells in soft tissue. Application of thistechnique ex vivo and in vivo to ablate unwanted cells can be useful fortreatment of aggressive, infiltrative and circumscribed neoplasms, aswell as a wide variety of applications in tissue engineering, tissueregeneration, and organ transplantation employing biologically-derivedtissue constructs.

SUMMARY OF THE INVENTION

The present invention provides novel applications of irreversible andreversible electroporation through the use of existing vasculaturewithin tissues as the conduit for pulse delivery. This methodologyresults in the separation of “electrodes” of just a few microns,reducing the energy necessary to induce non-thermal ablation of cellsand tissues to drastically improve preservation of the extracellularmatrix for the development of vascularized tissue constructs. Alsoprovided are clinical implications in the treatment of solid tumors andother in vivo applications, including ones that harness the reversiblerealm of electroporation, where the electrical fields temporarilyincrease the permeability of the cells without killing them,facilitating the intracellular transport of exogenous agents.

Use of IRE to decellularize tissue provides a controlled, precise way todestroy cells of a tissue or organ, while leaving the underlyingextracellular matrix (ECM), including vascularization and other grossmorphological features of the original tissue, intact. Thedecellularized scaffolds are then suitable for seeding with cells of theappropriate organism.

Where the process is performed ex vivo, the seeded tissue is suitablefor implantation into the organism as replacement tissue. In addition tomethods of producing scaffolds, the invention also provides thedecellularized scaffolds themselves, as well as methods of fabricationof engineered tissues and organs built from such scaffolds. Furthermore,the invention provides for use of the engineered scaffolds and theengineered tissues and organs built from such scaffolds.

More specifically, IRE can be used to focally ablate tissue whileleaving the microvasculature intact, using active perfusion of theorgan, optionally in combination with administering IRE using the organvasculature as a pathway for the electrical field. This innovativemethodology of using the vasculature as a pathway for IRE pulse deliveryis a promising solution for treating tumors embedded deep within tissue(e.g., treating from the inside out) or for full organ scaffoldgeneration.

It is known that plate electrodes and needle type electrodes can be usedto deliver IRE to treat tissues and organs. In some cases, however,plate electrodes may not be a preferred solution in ablating tumors ortreating organs deep within the organ. For example, plate electrodes aregenerally placed on an external surface of the organ and may causeunwanted damage to healthy tissue located between the tumor and theoutside surface of the organ. Needle electrodes are a viablealternative, as the needles are inserted into the organ to treat a moreinternal portion of the organ. The needle electrodes, while appearing tobe most effective at delivering treatments, must puncture the organ.Additionally, the low thermal dose requirement limits the maximumtreated area for each set of treatments and a large number of needlepunctures would normally be required to treat the entire organ. Evenfurther, these punctures provide an alternative path for fluids thuscompromising perfusion of downstream organ sections. Plate electrodescan be employed to mitigate some of these issues, but introducelimitations of their own. Large plate electrodes can be used to treatconsiderable sections of liver in one treatment. However, the voltage todistance ratio of an applied treatment will vary greatly over thetreated area due to changes in tissue depth. Protocols involving thesedelivery systems typically lead to compromises which may result ininadequate treatment of the organ.

As an alternative to plate and needle type electrodes, the inventorsprovide devices, systems, and methods for delivering electrical pulsesthrough the vasculature of a mechanically perfused organ to inducenon-thermal cell death in bulk tissue (e.g., liver tissue).

A representative device for administering IRE directly into thevasculature of an organ is shown in FIG. 1, which is a schematic diagramof an embodiment of an IRE mechanical perfusion connection device 10according to the invention. Connections to the vasculature 15 and theperfusion system can be made through the use of Luer lock connections20. A one way valve 25 inside the device can be used to preventback-flow and electrically isolate the organ between mechanicallysimulated heart beats. The device can comprise electrode 30 and anexternal electrode 40. Accordingly, such electroporation systems can beconnected internally to blood vessels and conductance structures(example: the hepatic vein, hepatic artery, portal vein, and/or bileduct of a liver) such that it does not impede continuous mechanicalperfusion. In such preferred focal ablation systems, the protocols caninduce cell death of 95% of cells while preserving the extracellularbasement membrane of lobule units.

Application of electrical energy through the vascular bed of ex vivo andin vivo tissues can be used to ablate unwanted cells as a means to treatdisease and create useful biologically-derived tissue constructs. Inaddition, this technique can be used to deliver electrical or thermalenergy to entire organs (or specific regions) to facilitate otherphenomenon. Other therapeutic treatments that can also be appliedthrough the vasculature include reversible electroporation forelectro-chemotherapy and electro-gene-therapy, radio frequency ablation,RF induced hyperthermia, and pulsed nanosecond electric fields. Indeed,any therapy that requires a conductive path to deliver energy can beadapted by applying the inventive principles disclosed in thisspecification.

Embodiments of the invention provide methods wherein the application ofvarying amounts of energy (both reversible and irreversibleelectroporation) (e.g., using the vasculature of an organ as conductivepathways) can be modulated to produce a wide range of desirable tissueablation effects, including selective removal of normal and neoplasticcells.

Application of varying amounts of energy using the vasculature of theorgan as conducive pathways can be used for other therapeutic modalities(e.g., electrochemotherapy (ECT), electrogenetherapy (EGT), nanosecondpulsed electric fields (nsPEF), High-frequency IrreversibleElectroporation (H-FIRE), radio frequency ablation, or acutehyperthermia) to achieve desirable therapeutic effects.

According to the invention, the effects of energy application (e.g.,using the vasculature of an organ as conductive pathways) can becontrolled and manipulated by varying the pulse shape, voltage,amperage, duration, repetition rate, and frequency of the energy and/orby the design and positioning of the energizing system.

Other aspects of the invention include controlling and manipulating theeffects of energy application (e.g., using the vasculature of an organas conductive pathways) through the design and use of sophisticated,precision-controlled vascular perfusion systems.

Methods of controlling the effects of energy application, e.g., throughpulsed electric fields, according to the invention can include varyingthe physiology-emulating characteristics of sophisticated,precision-controlled vascular perfusion systems.

Even further, the effects of energy application, e.g., through pulsedelectric fields, can be controlled by varying conditions of perfusionand preservation of ex vivo organs and tissues.

Energy application using IRE, e.g., through pulsed electric fields, andits resultant effects can be controlled by varying the conditions ofperfusion and preservation of in vivo organs and tissues according toembodiments of the present invention.

The invention also includes methods of controlling the effects of energyapplication, e.g., using the vasculature of the organ as conductivepathways, by varying the composition of intravascular fluids thatfunction partially or wholly as extensions of the energy applicationsystem and protocols.

More particularly, aspects of embodiments of the invention include thefollowing aspects, or combinations thereof. In a first aspect, includedis a method of ablating cells comprising: placing one or more electrodein, on, or near an organ or tissue; mechanically perfusing the tissue ororgan with a perfusate; and administering an electrical field into thetissue or organ for a sufficient time and at sufficient power to causeelectroporation of target cells. In a second aspect, such methods cancomprise: inserting the electrode(s) into vasculature of an organ ortissue; mechanically perfusing the tissue or organ with a perfusatethrough the vasculature; and administering an electrical field into thevasculature for a sufficient time and at sufficient power to causeelectroporation of target cells.

In a third aspect, such methods can comprise inserting a first electrodeinto an artery of the organ and a second electrode into a vein of theorgan and electroporating tissue or cells between the electrodes throughthe vasculature of the organ. Additionally or alternatively, otherphysiological pathways, such as the ureter or common bile duct can beused to apply energy. Such methods can comprise non-thermal irreversibleelectroporation of target cells.

A fifth aspect includes any of aspects 1-4, further comprising removingcellular debris from the tissue or organ by mechanical perfusion,physiological perfusion, or physical, chemical, or enzymatic techniques,or any combination thereof.

In a sixth aspect, a tissue scaffold formed from ablation of targetcells from a natural tissue source by administering irreversibleelectroporation to the target cells during perfusion of the tissue isprovided by embodiments of the invention. In a seventh aspect, suchscaffold of aspect 6 can comprise electroporation administered throughvasculature of the tissue. In an eighth aspect, the scaffold of aspect 6or 7 can comprise an extracellular matrix and vascular structure of anatural tissue source. In a ninth aspect, the scaffold of any of aspects6-8 can result in the tissue scaffold having a thickness in at least onedimension of about 1-8 cm, or 5-10 cm.

A tenth aspect includes an engineered tissue formed from ablation oftarget cells from a natural tissue source by administering irreversibleelectroporation to the target cells during perfusion of the tissue toobtain a tissue scaffold, and reseeding the scaffold with living cellsunder conditions that permit growth of the living cells on or in thescaffold.

In an eleventh aspect, the engineered tissue of aspect 10 can compriseelectroporation administered within vasculature of the natural tissue.In a twelfth aspect, the engineered tissue scaffold of aspect 10 or 11can comprise a tissue scaffold from an animal (any animal includinghuman) and living cells from a human. A thirteenth aspect includes theengineered tissue scaffold of any of aspects 10-12, wherein the tissuescaffold comprises an extracellular matrix and vascular structure of anatural tissue source. A fourteenth aspect includes the engineeredtissue scaffold of any of aspects 10-13, wherein the engineered tissuescaffold has a thickness in at least one dimension of about 1-10 cm. Afifteenth aspect can comprise the engineered tissue scaffold of any ofaspects 10-14, which is a heart, a lung, a liver, a kidney, a pancreas,a spleen, a gastrointestinal tract, a urinary bladder, a prostate, anovary, a brain, an ear, an eye, or skin, or a portion thereof, or anyother organ or portion thereof.

In a sixteenth aspect of the invention, included is a device forablating target cells of a tissue or organ comprising: a perfusionsystem adapted for delivering a perfusate from an artery to a vein ofthe tissue or organ vasculature; a first and second electrode eachadapted for insertion respectively into the artery and the vein of thetissue or organ vasculature; and a voltage source in operablecommunication with the electrodes for applying a voltage between thefirst and second electrodes during perfusion at a voltage and for a timesufficient to perform electroporation of target cells disposed betweenthe first and second electrodes. In a seventeenth aspect of theinvention, the device of aspect 16 can comprise electroporation that isnon-thermal irreversible electroporation. In an eighteenth aspect of theinvention, the device of aspect 16 or 17 can comprise electroporationthat is reversible in conjunction with adjuvant macromolecules in theperfusate (either in vivo in a patient's blood or ex vivo in a syntheticperfusate) to promote secondary effects to the electroporated cells.

In a nineteenth aspect, the electrodes can be inserted as described inaspect 3 in living tissue where the electrical energy parameters appliedthrough the targeted region are set to intentionally induce an increasein temperature to induce transport as in mild hyperthermia or thermaldestruction of the tissue (radiofrequency ablation).

In a twentieth aspect of embodiments of the invention, any aspect of theinvention can be adapted to be performed in a living animal or organunder mechanical perfusion wherein electric pulses are administered toinduce an electrical field through the vasculature for a sufficient timeand at sufficient power to cause electroporation of target cells tofacilitate the introduction of therapeutic gene constructs to treat adisease occurring within the targeted region. Such therapies would behelpful in terms of administering gene therapy, e.g., for islets ofpancreas in Type I diabetics to spur production of insulin (diseasedtissue, non-cancerous).

In a twenty-first aspect of the invention, any aspect of the inventioncan be adapted to be performed in a living animal or organ undermechanical perfusion wherein electric pulses are administered to inducean electrical field through the vasculature for a sufficient time and atsufficient power to cause electroporation of target cells to facilitatethe introduction of gene constructs to alter the cells to treat asystemic disease. Such therapies are applicable in the context ofimmunomodulation by introducing genes into tissue such as muscle toproduce desired antibodies (healthy tissue used as vessel for therapy).

In a twenty-second aspect of the invention, any aspect of the inventioncan be adapted to be performed in a living animal or organ undermechanical perfusion wherein electric pulses are administered to inducean electrical field through the vasculature for a sufficient time and atsufficient power to cause electroporation of target cells to facilitatethe introduction of therapeutic macromolecules to treat a disease,either within the targeted region or a systemic disease. Such therapiesare useful for increasing drug uptake to treat any range of diseases—notjust to kill cancer cells, but also any other drugs that could treat anon-cancerous disease. This aspect is similar to aspects 20 and 21, butwith drugs instead of genes.

In a twenty-third aspect of the invention, any aspect of the inventioncan be adapted to be performed in a living animal or organ undermechanical perfusion wherein administration of alternating electricfields through the vasculature produces thermal ablation of a targetedregion or entirety of an organ.

In a twenty-fourth aspect, any of the methods of aspects 1-23 caninclude a therapy selected from electrochemotherapy (ECT),electrogenetherapy (EGT), nanosecond pulsed electric fields (nsPEF),High-frequency Irreversible Electroporation (H-FIRE), radio frequencyablation, or acute hyperthermia.

A twenty-fifth aspect includes methods of any other aspect describedherein, comprising or further comprising administering an energy intothe vasculature for a sufficient time and at sufficient power to causedeath of target cells.

A twenty-sixth aspect is a method of any other aspect described herein,wherein a first electrode is inserted into a blood vessel of the organand a second electrode is inserted into another blood vessel of theorgan and electroporation is administered between the electrodes throughthe vasculature of the organ.

Likewise, a twenty-seventh aspect is a method of any other aspectdescribed herein, wherein a first electrode is inserted into a bloodvessel of the organ and a second electrode is inserted into a fluid ductof the organ and electroporation is administered between the electrodesthrough the vasculature of the organ.

Even further, a twenty-eighth aspect of the invention is a method of anyother aspect described herein, wherein a first electrode is insertedinto a blood vessel of the organ, a second electrode is inserted intoanother blood vessel of the organ, with a treatment region of the organdisposed between the first and second blood vessel, and electroporationis administered between the electrodes through the vasculature of theorgan.

A twenty-ninth aspect includes a method of any aspect described herein,wherein a first electrode is inserted into a blood vessel of the organand a second external grounding pad, plate electrode, or conductive gelexternal to the organ is used as a second electrode and electroporationis administered between the electrodes through the vasculature of theorgan.

Aspects of the invention can comprise electroporation to inducenon-thermal irreversible electroporation of target cells. Any aspect ofthe invention can be adapted to comprise removing cellular debris fromthe tissue or organ by mechanical perfusion, physiological perfusion, orphysical, chemical, or enzymatic techniques, or any combination thereof.Even further, any aspect of the invention can be adapted to furthercomprise monitoring through electrical measurements to detect andmonitor electroporation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain aspects of some of theembodiments of the present invention, and should not be used to limit ordefine the invention. Together with the written description the drawingsserve to explain certain principles of the invention.

FIG. 1 is a schematic diagram of an embodiment of an IRE-mechanicalperfusion connection device according to the invention.

FIG. 2 is a graph showing electric potential and electric field contoursdeveloped in a numerical representation of previous experiments.

FIGS. 3A-B are graphs showing numerical results of two differentsimulations with lobule level details (Model 2) where: (FIG. 3A)External Electrodes are charged with either 1500V (top) or set to ground(bottom), and (FIG. 3B) Central venula of each lobule is charged to1500V while external electrodes are grounded.

FIG. 4A is a diagram showing simulated electric field distribution witha single lobule when a 50V 100 microsecond pulse is administered to thebile duct and the central venule, portal venule and portal arteriole aregrounded.

FIG. 4B is a schematic representation of a liver lobule illustrating thecomplex vascular network of these functional units (see Slieman, T. A.The Digestive System,http://tonyslieman.com/phgy_230_lecture_digestive.htm).

FIGS. 5A-B are drawings of (FIG. 5A) placement of the electrodes onactively perfused liver tissue and (FIG. 5B) the resultant lesion aftertreatment with 99, 100 μs, 1500V/cm pulses and 4 hours of perfusion,with the approximate area of the electrode is outlined in black.

FIGS. 6A-C are schematic diagrams of the numerical model used todetermine treatment electric field thresholds, with numerical resultsdepicting an electric field of 379±142 V/cm within the treatment margin.

FIGS. 7A-B are graphs showing that lesions that developed after pulsesapplied at 1 Hz were statistically larger (α=0.1) than lesions whichdeveloped at rates of 0.25 and 4 Hz.

FIGS. 8A-B are micrographs showing a histological comparison ofuntreated liver tissue to areas which have undergone mild IRE treatmentsshowing preservation of connective tissue and blood vessels.

FIGS. 9A-C are micrographs showing (FIG. 9A) A section of untreatedliver after 24 hours of perfusion. Sections of the same liver treatedwith 90, 1500V/cm, 100 μs pulses at 4 Hz using needle electrodes after24 hours of perfusion at (FIG. 9B) 10 x and (FIG. 9C) 20× magnification.

FIGS. 10A-B are micrographs showing (FIG. 10A) A section of untreatedliver after 24 hours of perfusion and (FIG. 10B) the same liver treatedwith 100, 1500V/cm, 100 μs pulses at 1 Hz using needle electrodes after24 hours of perfusion at 20× magnification.

FIG. 11 is a drawing of a perfusion electrode according to theinvention.

FIG. 12 is a drawing showing a kidney simultaneously attached to theprototype electrodes and perfusion system by way of the renal vein andartery.

FIG. 13 is a graph showing impedance measurements from the kidney priorto pulsing, which presented a significant electrical resistance andcapacitance.

FIG. 14 is a drawing of a monitor output showing a resultant waveformfrom a 50 microsecond pulse with amplitude of 1000V.

FIG. 15 is a graph showing the maximum current delivered and decay timefor pulses delivered with amplitudes between 100 and 2000 V.

FIG. 16 is a drawing showing a kidney section 30 minutes after pulsing,wherein area 80 indicates live tissue and area 84 indicates regionsablated by the IRE pulses.

FIG. 17 is a drawing depicting placement of one electrode, where onedevice is disposed in an artery.

FIG. 18 is a drawing depicting placement of one electrode, where onedevice is disposed in a vein.

FIG. 19 is a drawing depicting placement of one electrode, where onedevice is disposed in a bile duct.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to various exemplary embodiments ofthe invention. It is to be understood that the following discussion ofexemplary embodiments is not intended as a limitation on the invention.Rather, the following discussion is provided to give the reader a moredetailed understanding of certain aspects and features of the invention.

According to embodiments of the invention, viable decellularized tissuescaffolds can be attained using non-thermal irreversible electroporation(N-TIRE) on organs under continuous perfusion. Electroporation(reversible and/or irreversible) can be delivered to tissues and organsusing any known techniques, including plate electrodes or needleelectrodes, or even delivering the electrical charge through thevasculature of an organ or tissue.

More specifically, electroporation can be used as a therapy to treatnumerous medical conditions. Irreversible Electroporation, includingnon-thermal IRE, is a method to kill undesirable cells using electricfields in tissue while preserving the ECM, blood vessels, and nerves.Certain electrical fields, when applied across a cell, have the abilityto permeabilize the cell membrane through a process that has come to becalled “electroporation.” When electrical fields permeabilize the cellmembrane temporarily, after which the cells survive, the process isknown as “reversible electroporation.” Reversible electroporation hasbecome an important tool in biotechnology and medicine. Other electricalfields can cause the cell membrane to become permeabilized, after whichthe cells die. This deadly process is known as “irreversibleelectroporation.” Non-thermal irreversible electroporation is a new,minimally invasive surgical technique to ablate undesirable tissue, forexample, tumor tissue. The technique is easy to apply, can be monitoredand controlled, is not affected by local blood flow, and does notrequire the use of adjuvant drugs. The minimally invasive procedureinvolves placing needle-like electrodes into or around the targeted areato deliver a series of short and intense electric pulses that inducestructural changes in the cell membranes that promote cell death. Thevoltages are applied in order to electroporate tissue without inducingsignificant joule heating that would significantly damage major bloodvessels and the ECM. For a specific tissue type and set of pulseconditions, the primary parameter determining the volume irreversiblyelectroporated is the electric field distribution within the tissue.Recent IRE animal experiments have verified the many beneficial effectsresulting from this special mode of non-thermal cell ablation, such aspreservation of major structures including the extracellular matrix,major blood vessels, and myelin sheaths, no scar formation, as well asits promotion of a beneficial immune response.

Electroporation is a non-linear biophysical process in which theapplication of pulsed electric fields leads to an increase inpermeability of cells, presumably through the creation of nanoscalepores in the lipid bilayer. Weaver, J. C., Electroporation of biologicalmembranes from multicellular to nano scales, IEEE Trns. Dielectr.Electr. Insul. 10, 754-768 (2003). If the length and intensity of thepulses do not exceed certain criteria, this permeability is reversibleand cellular health and function is maintained. Once a critical electricfield intensity threshold is surpassed (approx. 500 to 700V/cm for atypical set of pulse parameters) the cell membrane is unable to recoverand cell death is induced. See Garcia, P. et al. Intracranial nonthermalirreversible electroporation: in vivo analysis. J Membr Biol 236,127-136 (2010); Sel, D. et al. Sequential finite element model of tissueelectropermeabilization. Ieee Transactions on Biomedical Engineering 52,816-827, doi:10.1109/tbme.2005.845212 (2005); and Lee, E. W. et al.Advanced Hepatic Ablation Technique for Creating Complete Cell Death:Irreversible Electroporation. Radiology 255, 426-433,doi:10.1148/radiol.10090337 (2010) (“Lee 2010”).

The application of pulses that permanently destabilize the membranes ofthe cells, inducing death in a precise and controllable manner withsub-millimeter resolution (Edd, J. F., Horowitz, L., Davalos, R. V.,Mir, L. M. & Rubinsky, B. In vivo results of a new focal tissue ablationtechnique: Irreversible electroporation. Ieee Transactions on BiomedicalEngineering 53, 1409-1415, doi:10.1109/tmbe.2006.873745 (2006)) is aprocess referred to as non-thermal irreversible electroporation (N-TIRE)(Davalos, R. V., Mir, L. M. & Rubinsky, B. Tissue ablation withirreversible electroporation. Annals of Biomedical Engineering 33,223-231, doi:10.1007/s10439-005-8981-8 (2005) (“Davalos 2005”)). Thetechnique does not rely on thermal mechanisms (Davalos 2005) and hasbeen shown to preserve the structure of the underlying extracellularmatrix. Studies show that nerve conduits and bile ducts are not damagedwithin the ablation zones. Maor, E., Ivorra, A., Leor, J. & Rubinsky, B.The effect of irreversible electroporation on blood vessels. Technologyin Cancer Research & Treatment 6, 307-312 (2007). Additionally, in vivoliver ablation regions showed minimal damage and minor vasculitis insmall vessels. (Lee 2010).

Hypothermic oxygenated perfusion (HOPE), is a method of whole organpreservation which mechanically delivers an oxygenated, nutrient-richblood substitute to an entire organ at sub-physiological temperatures.See Dutkowski, P., de Rougemont, O. & Clavien, P. A. Machine perfusionfor ‘Marginal’ liver grafts. Am. J. Transplant. 8, 917-924,doi:10.1111/j.1600-6143.2008.02165.x (2008); and Monbaliu, D. & Brassil,J. Machine perfusion of the liver: past, present and future. Curr. Opin.Organ Transpl. 15, 160-166, doi:10.1097/MOT.0b013e328337342b (2010).This method has been successfully demonstrated to improve thepreservation quality and transplant success rates of kidneys which haveundergone warm ischemia (see Olschewski, P. et al. The influence ofstorage temperature during machine perfusion on preservation quality ofmarginal donor livers. Cryobiology 60, 337-343,doi:10.1016/j.cryobiol.2010.03.005 (2010); and Stegemann, J., Hirner,A., Rauen, U. & Minor, T. Use of a New Modified HTK Solution for MachinePreservation of Marginal Liver Grafts. Journal of Surgical Research 160,155-162, doi::10.1016/j.jss.2008.10.021 (2010)) with research strivingto reach 72 hour preservation times (Yamamoto, N. et al. 72-HourPreservation of Porcine Liver by Continuous Hypothermic Perfusion withUW Solution in Comparison with Simple Cold Storage, Journal of SurgicalResearch 51, 288-292 (1991). Schon et al. and Brockmann et al. havedemonstrated the ability to prolong organ quality using normothermicperfusion, a process in which the perfused fluid is held at or nearphysiological temperatures. See Schon, M. R. et al. Livertransplantation after organ preservation with normothermicextracorporeal perfusion. Annals of Surgery 233, 114-123 (2001); andBrockmann, J. et al. Normothermic Perfusion A New Paradigm for OrganPreservation. Annals of Surgery 250, 1-6,doi:10.1097/SLA.0b013e3181a63c10 (2009).

These methods of organ preservation can be used to isolate N-TIRE tissueablation effects from the immune response observed in vivo and thenatural degradation of tissue post mortem. Recently, it has beendetermined through the use of translational laboratory models thatcapitalizing on the ability of N-TIRE to destroy cells withoutdestroying the extracellular matrix (Davalos, R. V. IrreversibleElectroporation to Create Tissue Scaffolds. United States patent (2009);and Phillips, M., Maor, E. & Rubinsky, B. Non-Thermal IrreversibleElectroporation for Tissue Decellularization. J. Biomech. Eng,doi:10.1115/1.4001882 (2010)) renders N-TIRE a viable means for scaffoldcreation by way of organ decellularization.

N-TIRE treatment outcomes can be predicted through numerical modelingtissue ablation/decellularization, which is clinically relevant andcould be widely applied for tissue engineering. See Davalos, R. V. &Rubinsky, B. Temperature considerations during irreversibleelectroporation. International Journal of Heat and Mass Transfer 51,5617-5622, doi:10.1016/j.ijheatmasstransfer.2008.04.046 (2008); Edd, J.F. & Davalos, R. V. Mathematical Modeling of irreversibleElectroporation for treatment planning. Technology in Cancer Research &Treatment 6, 275-286 (2007); and Neal, R. E., II & Davalos, R. V., TheFeasibility of Irreversible Electroporation for the Treatment of BreastCancer and Other Heterogeneous Systems. Annals of Biomedical Engineering37, doi::10.1007/s10439-009-9796-9 (2009).

Engineered scaffolds could then be reseeded with a recipient's cells,resulting in a functional organ construct. Such methods of organregeneration might be used to decrease the shortage in supply of organsfor transplant.

Embodiments of the present invention relate to methods, systems, anddevices for the delivery of Irreversible Electroporation (IRE) throughthe vasculature of organs. IRE administered in this manner whether exvivo or in vivo can be used to treat tumors embedded deep withinvascularized organs. Applications of embodiments of the invention alsoinclude use of IRE through the vasculature of tissues and organs todecellularize organs and produce a scaffold from existing tissue withthe extracellular matrix intact and cellular debris removed.

Generally, ablation procedures involve delivering a series of low energy(intense but short) electric pulses to the targeted tissue. These pulsesirrecoverably destabilize the cell membranes of the targeted tissue,thereby killing the cells affected by the electrical field. Thetreatment is non-thermal, essentially only affects the cell membranes ofthe targeted tissue, and does not affect the nerves or blood vesselswithin the treated tissue.

The present invention provides decellularized scaffolds, which can becreated using non-thermal irreversible electroporation (IRE). The organor tissue can be perfused during and/or after the procedure, which is aroutine technique in the medical arts.

Following preparation of a scaffold, tissue engineering can involve exvivo seeding and attachment of human cells onto a scaffold. To date, themost successful scaffolds for tissue engineering have been natural andmade by chemically and/or mechanically decellularizing organs of largeanimals (e.g., pigs).

Embodiments of the invention provide methods of making a decellularizedtissue scaffold. In general, tissue comprising cells and an underlyingscaffold can be treated in vivo or ex vivo with an electrical field ofsufficient power and duration to kill cells of the tissue. Theelectrical field is administered directly into the vasculature of theorgan. The electrical field is guided through the vasculature of theorgan by the walls of the vascular system. Preferably, the electricalpulses are administered in a manner to avoid disruption to theunderlying scaffold and vasculature of the organ or tissue.

The methods are suitable for producing a tissue scaffold for use intissue engineering. Although the source of the tissue is not limited, inexemplary embodiments, the tissue is from a relatively large animal oran animal recognized as having a similar anatomy (with regard to thetissue of interest) as a human, such as a pig, a cow, a horse, a monkey,or an ape. In embodiments, the source of the tissue is human, use ofwhich can reduce the possibility of rejection of engineered tissuesbased on the scaffold.

In preferred embodiments, the method leaves intact vascular structuresof the tissue, such as capillaries. In embodiments, the method leavesintact neural tubes present in the tissue before treatment with theelectrical field. As used herein, the term “intact” refers to a state ofbeing whereby an element is capable of performing its original functionto a substantial extent. Thus, for example, an intact capillary is acapillary that is capable of carrying blood and an intact neural tube isa tube that can accommodate a neuron. In embodiments, cells of thevascular system and neural system remain intact, as well as otherglandular structures, including examples such as bile or lactiferousducts. In such embodiments, the cells can remain as part of the scaffoldand engineered tissue, or may be removed by suitable treatmenttechniques or by cells that are seeded onto a scaffold or by cells of abody that receives the engineered tissue.

According to method embodiments of the invention, a tissue is exposed toan electrical field that is adequate in time and power to cause killingof cells of the tissue, but not adequate to significantly destroy thescaffolding upon and within which the cells exist. Furthermore, inpreferred embodiments the electrical field does not cause irreversibletissue damage as a result of heating of the tissue. Various ways ofproviding such an electrical field are possible. In typical embodiments,one or more electrical pulses are applied to the tissue to cause cellmembrane disruption as a result of the electricity and not substantiallyas a result of heat. Where two or more pulses are used, the pulses areseparated by a period of time that allows, among other things, thetissue to cool so that thermal damage does not occur to a significantextent. For example, one or more electrical pulses can be applied to thetissue of interest for a duration in a range from about 5 microseconds(μs) to about 200 seconds and pulses may be applied at lower repetitionrates over periods of 1 to 24 hours. For convenience, a short period oftreatment might be desired. As such, in preferred embodiments,electrical pulses are applied for a period of about 1-10000 μs. Further,although there is no limit on the number of pulses to be delivered tothe tissues, in preferred embodiments, from about 1 to about 100 pulsesare applied to the tissue. For example, in an exemplary embodiment,about 10-1000 pulses of about 100 μs each in duration are applied to thetissue to cause cellular ablation.

Organs can then be treated to create a decellularized scaffold byadjusting perfusion parameters to remove cellular debris. Mechanicalcleansing of cellular debris can be performed for any amount of timenecessary to achieve the desired results of removal of the debris, forexample, over periods of 4, 12, 24, 48, or 72 hours. Perfusionparameters including systolic pressure, diastolic pressure, andtemperature can be manipulated to improve the efficiency of removal ofcellular debris. Further, mild detergents may be added if necessary toenhance or facilitate removal of the cellular debris. Preferredembodiments provide for perfusion protocols which result in the removalof 99% of cellular debris and DNA constituents.

Embodiments of the invention provide methods wherein the application ofvarying amounts of energy (both reversible and irreversibleelectroporation) can be modulated to produce a wide range of desirabletissue ablation effects, including selective removal of normal andneoplastic cells.

According to the invention, the effects of energy application can becontrolled and manipulated by varying numerous parameters including,e.g.: the voltage, amperage, duration, and frequency of the energy; thedesign and positioning of the energizing system; the design and use ofsophisticated, precision-controlled vascular perfusion systems; thephysiology-emulating characteristics of sophisticated,precision-controlled vascular perfusion systems; the conditions ofperfusion and preservation of ex vivo organs and tissues; the conditionsof perfusion and preservation of in vivo organs and tissues; and/or thecomposition of intravascular fluids that function partially or wholly asextensions of the energy application system and protocols.

In this effort, there are several parameters that can be monitored andadjusted in using non-thermal IRE for preparation of tissue scaffolds,or for treating tumors in vivo or ex vivo, or for ensuring adequatemacromolecule biotransport in diseased or otherwise targeted tissues.For example, embodiments of the invention can be used in gene therapyfor islets of pancreas in Type I diabetics to spur production ofinsulin, i.e., a situation where there is non-cancerous diseased tissue.The invention can also be applicable to immunomodulation by introducinggenes into tissue such as muscle to produce desired antibodies, i.e.,healthy tissue used as vessel for therapy. Parameters that can be variedfor particular applications include voltage gradient. In embodiments,the pulses produce a voltage gradient in a range of from about 10volt/cm to about 10,000 volt/cm. Voltage gradient (electric field) is afunction of the distance between electrodes and electrode geometry,which will vary depending on the size of the tissue sample, tissueproperties, and other factors. In some embodiments, two electrodes areused, and they are placed about 5 mm to 10 cm apart. Typical electrodediameters range from 0.25-1.5 mm and typically 2 or 4 electrodes areused. In embodiments, one bipolar electrode is used. Also, the“electrode” can have parts of it insulating (including using anon-conductive sheath) and parts of it conductive (e.g., at the tip) toensure proper application of the electrical current and to minimizeproduction of excessive heat in parts of the tissue.

Appropriate electrical fields and durations of exposure are those thathave been reported in the literature as being suitable for medicaltreatment of tissues for tumor ablation. Exemplary exposure parametersinclude: ninety 90 microsecond (μs) pulses at 1.5 kV/cm at a frequencyof 1 Hz or 4 Hz; eighty 100 μs pulses at 2.5 kV/cm at a frequency of 1Hz or 4 Hz; one 20 millisecond pulse at 400V/cm; ten 100 μs pulses at3800 V/cm at a frequency of 10 pulses per second; ninety 100 μs pulsesranging from 1000 to 1667 V/cm at a frequency of about 1 Hz or 4 Hz; andeighty pulses of 100 μs ranging from 1000 to 3000 V/cm at about 1 Hz or4 Hz. In general, the frequency of pulsing can be as low as half thepulse width and can be quite a bit farther apart. Any suitable frequencythat allows for electroporation without significant thermal damage tothe tissue is acceptable. Electrical current can be supplied as eitherDC or AC. Indeed, it is within the skill of the art to adjust theseparameters as applicable to achieve a particular desired result. Anynumber of pulses can be administered, for example, from 1-1000. Thepulses can have a duration of any amount of time, such as from 1microsecond to 1 second. The voltage can be any amount to achievereversible or irreversible electroporation depending on the desiredeffect and can include for example from 500V/cm to 5000 V/cm, e.g., 1500V/cm. Indeed, to achieve IRE at the capillary bed, much less voltage isrequired, e.g., on the order of about 1 V/cm up to about 1000 V/cm.

The shape and size of the electrodes are not critical to practice of theinvention. Those of skill in the art may choose any shape and size thatis suitable for transmitting the desired electrical field into thetissue. For example, the electrodes may be plate type, wire type, orneedle type and may be circular in shape, ovoid, square, rectangular,diamond-shaped, hexagonal, octagonal, etc. For wire type electrodes, adiameter smaller than the vasculature in which the wire is to beinserted is desired, such that the electrode does not occludevasculature. In some designs and manifestations, it may be desirable touse electrodes that are part of an occlusive device providing isolationof a portion of the circulation of an organ or tissue. Likewise, thesurface area of the electrodes is not critical to practice of theinvention. Thus, for example, the surface area may be about 0.5 squarecentimeter, about 1 square centimeter, or greater. For electrodesinserted directly into the vasculature of an organ or tissue, preferablythe electrodes are elongated wire type electrodes of a sufficient lengthto provide the electrode a sufficient distance within the vasculature.The diameter of the wire type electrode can also be adapted forinsertion into various types of organ vasculature such that theelectrode preferably avoids contact or has minimal contact with theinterior walls of the vasculature. In some embodiments, there is atleast some separation between the electrodes and the walls of thevasculature. In the wire type electrode, it is possible to temporarilyocclude the vessels “upstream” and “downstream” of the targeted regionto reduce the potential for electrical current and associated energylosses traveling beyond the bounds of the targeted region between theelectrodes. Such an embodiment performed in vivo should deliver thepulses within a time period that will not induce unacceptable ischemiceffects to the targeted and any “downstream” regions. More particularly,such techniques can include clamping the vessels above and below thetargeted organ or tissue so that the rest of the vessels do not conductthe current (as clamping with the insulating vessel walls should “open”the circuit). This is more relevant for gene or drug deliveryapplications, where killing cells is not the goal, and there should be asuitable window to perform this without damaging the tissue. Suchmethods of the invention can be employed, for example, for plaqueremoval, e.g., occlude the carotid artery for about 10 minutes whileremoving plaque therefrom.

Exposing tissue to electrical fields in some circumstances generatesheat. To ensure that tissue damage due to heat is avoided, the amount ofenergy transmitted to the tissue is set below a threshold level per unittime. Time and temperature parameters are known in the art for IRE, andany suitable combination may be used. For example, the temperature ofthe tissue can be monitored during treatment for ablation, and theelectrical pulses adjusted to maintain the temperature at 100° C. orless, such as 60° C. or less, or at body temperature. In embodiments,the temperature can be maintained at a physiological temperature normalto a particular organ or subject. In some embodiments, the temperatureis maintained at 50° C. or less.

In some embodiments, the method includes adjusting the applied voltage,length of the pulses, and/or number of pulses to obtain irreversibleelectroporation averaged over the biological cells of the tissue,thereby achieving irreversible electroporation of the biological cellsin the tissue at a level that minimizes damage to non-target tissue.Protocols may include the same or varied parameters throughoutadministration of the electrical charge. Likewise, in some embodiments,the duration of the applied voltage is adjusted in accordance with thecurrent-to-voltage ratio to achieve irreversible electroporation ofidentified tissue cells, whereby cell membranes are disrupted in amanner resulting in cell death. Additional exemplary parameters aredisclosed below.

Example I—Multiphysics Modeling

Preliminary multiphysics modeling was conducted to establish thefeasibility of using the vascular system as a pathway for electricalpulse delivery. The electric field distribution, which is the key factorfor the development of pores (reversible or irreversible) in the cellmembrane, was modeled using a finite element method. Three liver tissuemodels were developed representing the liver structure with differentlevels of detail. The Comsol Multiphysics was used to solve for theelectric potential (ϕ) which obeys the Laplace Equation:

∇·(σ∇ϕ)=0

where σ is the electrical conductivity.

Model 1:

Initially, the liver was modeled as a 2 cm thick homogenous structurewith 1 cm diameter plate electrodes on either side of the tissue. Thismodel was used to correlate experimental lesions to electric fieldintensities. A single 10 microsecond 1500V/cm pulse was delivered to thetop electrode while the bottom electrode was grounded. As shown in FIG.2, the results of this model show that for the electrical parametersused, simulated electric field strength of approximately 400V/cm isrequired to generate a lesion of similar width to experimental results.

TABLE 1 Electrical conductivity values for elements used in all models.Conductivity Element (S/m) Liver  4.10E−01 Connective tissue  4.10E−02Perfusate  1.40E+00 External Electrodes 5.998E+07

Model 2:

The liver is a complex organ populated by numerous sets of vasculaturebranches, lymph and bile ducts. Branches of the hepatic portal vein andhepatic artery deliver blood to basic functional units, lobules whichare structurally functioned to filter blood, remove bacteria, andproduce bile. Blood driven through the lobules eventually reach a largecentral venula which drain into the hepatic vein and return blood to thecirculatory system. While under perfusion, a perfusate replaces blood asthe fluid traveling through the vasculature. It is noted, however, thatbile production has been observed to continue for up to 24 hours. Asecond multi-scale model was produced to understand how the complexvasculature affects the electric field distribution when two differentmodalities of voltage application are used. The first modality usedtraditional electrodes placed outside of the tissue, while the secondused the central venula as the voltage source and external electrodes asgrounds. Each lobule was modeled as a hexagon with an equivalent radiusof 1 mm surrounded by a 5 micron connective tissue layer and a 200micron diameter central venula which is consistent with swine histology.A single 10 microsecond 1500V/cm pulse was again simulated.

The electric field distribution within the tissue did not varysignificantly with the additional inhomogeneity caused by the lobuleepithelial layers when external electrodes are used. The mostsignificant alterations occurred in proximity to the more highlyconductive central venula. When the central venula of each lobule ischarged to 1500V, a significantly different electric field distributionis formed. Regions of tissue which reach a high enough electric field tobecome irreversibly electroporated extend only approximately 0.5 cm intothe tissue. Though this modality of electric field application is notsufficient for total decellularization, it may be an effective means bywhich tumors close to the surface of highly vascularized organs may betreated. The model presented in FIG. 3A shows the external electrodescharged with either 1500V (top) or set to ground (bottom), whichdemonstrated that the electric field distribution using this modalitydid not significantly change with the added inhomogeneity. The modelpresented in FIG. 3B shows the central venula of each lobule charged to1500V while external electrodes are grounded. It is noted that themodels presented in FIGS. 3A-B are not completely physiologically exactas fluid readily flows from the portal arterioles and venules throughthe lobule into the central venula.

Model 3:

Model 3 incorporates the portal arterioles, portal venules, and bileducts at the vertices of a single lobule. The central vein is surroundedby bulk liver tissue. The magnitude of the applied 10 microsecond pulsewas varied until an electric field distribution, in the range of thatseen in bulk liver tissue, developed.

Results from this simulation are shown in FIG. 4A. The results from thissimulation show that the development of an IRE inducing electric fieldwithin a single lobule is feasible using the organ's vasculature.Additionally, it was found that a 50V pulse is significant enough toraise the electric field to IRE inducing levels. This is far below the1500V pulse necessary to induce IRE when the electric field is appliedacross the entire tissue construct. It can be seen from FIG. 4B andhistological samples that there is a complex microvasculature networkwhich connects the portal arterioles and venules from the central vein.Between the vasculature there are hepatocytes which secrete bile intothe bile ducts. Models 1 and 2 assume that these microvasculaturenetworks present a significant resistance to the flow of current and theinternal constituents of the lobule can be modeled as a heterogeneoustissue. This is a reasonable assumption to make where vascular occlusionmay occur if erythrocytes (in vivo) or epithelial cells are damaged bythe electric field.

TABLE 2 Resistance of vessels of decreasing diameter with a 10:1 lengthto diameter ratio and a fluid conductivity of 1.4 S/m. Diameter AreaLength Resistance (m) (m²) (m) (ohms) 1.0E−02 7.85E−05 1.0E−01 9.09E+021.0E−03 7.85E−07 1.0E−02 9.09E+03 1.0E−04 7.85E−09 1.0E−03 9.09E+041.0E−05 7.85E−11 1.0E−04 9.09E+05

An approximation of the resistance (R) of vasculature andmicrovasculature can be easily achieved if the fluid conductivity (ρ) isknown by solving the constitutive relation:

$R = \frac{\rho \; L}{A}$

where L and A are the length of the vessel and the vessel's crosssectional area respectively. The results presented in Table 2 show thatthe resistance of a 10 μm diameter vessel 100 μm long can be as high as90 kΩ when the vessel is filled with phosphate buffered solution. Whilesignificant, this resistance is not high enough to prevent current flowthrough microvasculature. Additionally, the immense number ofmicrovessels which are connected in parallel throughout the organ shoulddrastically reduce the overall electrical resistance.

One embodiment of the invention is the preparation of scaffolds byadministering IRE during active perfusion of the organ or tissue.Electrodes can be placed into or near the vicinity of the tissue withthe application of electrical pulses causing irreversible (orreversible) electroporation of the cells through the target region. Oneway to administer the electrical pulses is through the vasculature ofthe organ itself. Placement of the electrodes defines the treatedregion; thus, the treated region may be only a portion of an entiretissue or organ that is used as the starting material. The electricpulses irreversibly or reversibly permeate the membranes of treatedcells, thereby invoking cell death (if irreversible). The length of timeof the electrical pulses, the voltage applied, and the resultingmembrane permeability are all controlled within defined ranges.Application of electric pulses that result in cell death can stillpreserve some or all of the vascular structures of the organ, preferablyincluding those involved in microcirculation and macrocirculation. Insome embodiments, microcirculation structures may be partially ortotally damaged, but larger structures maintained.

For in vitro and ex vivo practice of embodiments of the invention,secondary techniques for removing cellular material can be used. Forexample, any of the known physical, chemical, or enzymatic techniquescan be used to remove cellular debris from the irreversiblypermeabilized cells. Likewise, the treated tissue can be attached to anartificial perfusion system, which can pump a liquid composition (e.g.,a detergent-containing aqueous composition) through the treated tissue,resulting in removal of cell debris from the scaffold. Importantly, suchsecondary treatments, where applied, can be applied under relativelygentle conditions, which allow for removal of cellular debris but alsoretention of the scaffolding structure (including vascular and neuralstructures). The use of non-thermal IRE allows for such gentleprocedures, and improves the scaffold that is ultimately produced, ascompared to procedures not relying on non-thermal IRE.

For in vivo practice of the method, the debris remaining from theirreversibly permeabilized cells may be left in situ and may be removedby natural processes, such as the body's own circulation and immunesystem.

The concept of irreversible electroporation to decellularize tissues isdifferent from other forms decellularization used in the art.Irreversible electroporation is different from chemical and physicalmethods or cell lysis using osmotic imbalance because it useselectricity to kill the cells. Irreversible electroporation is a morebenign method because it destroys only the cell membrane of cells in thetargeted tissue and does not damage to the underlying extracellularmatrix (ECM). In contrast, chemical and physical methods can damagevital structures, such as the ECM, blood vessels, and nerves. IRE of thetype described here, uses electrical pulses to serve as the active meansfor inducing cell death by a specific means, i.e., by fatally disruptingthe cell membrane.

Irreversible electroporation may be used for the decellularizing tissuein a minimally invasive procedure that does not or does notsubstantially affect the ECM. Its non-selective mode ofdecellularization is acceptable in the field of tissue engineering andprovides results that in some ways are comparable to sonication,inducing an osmotic imbalance, freezing, or chemical decellularization.

One exemplary embodiment of the invention includes a method wherebycells of tissue are irreversibly electroporated by applying pulses ofvery precisely determined length and voltage during active perfusion ofthe organ or tissue. This may be done while measuring and/or observingchanges in electrical impedance in real time and noting decreases at theonset of electroporation and adjusting the current in real time toobtain irreversible cellular damage without thermal damage. The methodthus may include use of a computing device and sensors to monitor theeffects of the electrical treatment. In embodiments where voltage isapplied, the monitoring of the impedance affords the user knowledge ofthe presence or absence of pores. This measurement shows the progress ofthe pore formation and indicates whether irreversible pore formation,leading to cell death, has occurred.

Yet another embodiment includes a method whereby the onset and extent ofelectroporation of cells in tissue can be correlated to changes in theelectrical impedance (which term is used herein to mean the voltage overcurrent) of the tissue. At a given point, the electroporation becomesirreversible. A decrease in the resistivity of a group of biologicalcells occurs when membranes of the cells become permeable due to poreformation. By monitoring the impedance of the biological cells in atissue, one can detect the average point in time in which pore formationof the cells occurs, as well as the relative degree of cell membranepermeability due to the pore formation. By gradually increasing voltageand testing cells in a given tissue, one can determine a point whereirreversible electroporation occurs. This information can then be usedto establish that the cells of the tissue have undergone irreversibleelectroporation. This information can also be used to control theelectroporation process by governing the selection of the voltagemagnitude. Other imaging techniques can be employed to monitor how mucharea has been treated (e.g., ultrasound, MRI, CT, etc.).

The invention provides the simultaneous irreversible electroporation ofmultitudes of cells providing a direct indication of the actualoccurrence of electroporation and an indication of the degree ofelectroporation averaged over the multitude. The discovery is likewiseuseful in the irreversible electroporation of biological tissue (massesof biological cells with contiguous membranes) for the same reasons. Thebenefits of this process include a high level of control over thebeginning point of irreversible electroporation.

One feature of embodiments of the invention is that the magnitude ofelectrical current during electroporation of the tissue becomesdependent on the degree of electroporation so that current and pulselength are adjusted within a range predetermined to obtain irreversibleelectroporation of targeted cells of the tissue while minimizingcellular damage to surrounding cells and tissue. Yet another feature ofembodiments of the invention is that pulse length and current areprecisely adjusted within ranges to provide more than mere intracellularelectro-manipulation which results in cell death and less than thatwhich would cause thermal damages to the surrounding tissues. Anotherfeature of embodiments is that measuring current (in real time) througha circuit gives a measurement of the average overall degree ofelectroporation that the cells in the tissue achieve.

Yet other features of embodiments include that the precise electricalresistance of the tissue can be calculated from cross-time voltagemeasurement with probe electrodes and cross-current measurement with thecircuit attached to electroporation electrodes; the precise electricalresistance of the tissue is calculated from cross-time voltagemeasurement with probe electrodes and cross-current measurement with thecircuit attached to electroporation electrodes; and electricalmeasurements of the tissue can be used to map the electroporationdistribution of the tissue. It is noted that, in irreversibleelectroporation it is possible and perhaps even preferred to perform thecurrent or EIT measurements a substantial time (several minutes or more)after the electroporation to verify that it is indeed irreversible.

In embodiments of the method, it is preferred to remove cellular debrisfrom the decellularized scaffolding after primary cell destruction withnon-thermal IRE. In such embodiments, any known technique for doing somay be used, including any of the known physical, chemical, and/orenzymatic methods. In one exemplary embodiment, removal of cellularmaterial is accomplished, at least in part, through perfusion of thetissue scaffolding with an appropriate agent (e.g., water, pH-adjustedwater, an aqueous solution of one or more chelating agents, etc.), usinggeneral diffusion, transmittal via remaining intact vasculature, or amixture of the two.

For in vitro methods, it is preferred that the scaffold be sterilized,especially where the scaffold is to be used to prepare engineeredtissues and organs for implantation into a host. Sterilization and/orremoval of debris after decellularization is usually conducted forscaffolds that will be used as implants to reduce the risk of patientrejection (for example, due to DNA fragments). When a scaffold requiressome type of sterilization, methods published in the literature forsterilization of scaffolds can be employed.

For in vitro methods, the method of making a decellularized tissuescaffold results in a decellularized tissue scaffold that is isolatedfrom its natural environment. For in vivo methods, the method of makinga decellularized tissue scaffold results in a tissue scaffold that isdevoid of normal cellular material. Thus, in an aspect of the invention,an engineered tissue scaffold is provided. The engineered tissuescaffold comprises a natural scaffold that is removed from its naturalenvironment and/or from which cellular material has been removed. Theengineered tissue scaffold of the invention contains at least some,preferably most, and more preferably substantially all or all, of thevascular structures (i.e., arteries, veins, capillaries) and conductingstructures (i.e., ducts) present in the tissue in its natural state. Inembodiments, the tissue scaffold comprises at least some, preferablymost, and more preferably substantially all or all of the neuralstructures present in the tissue in its natural state. In embodiments,the scaffold further comprises the cells that constitute these vascularstructures and/or these neural structures. Preferably, the engineeredtissue scaffold contains a reduced number of the cells naturallypopulating the scaffold. A majority of the original cells, morepreferably substantially all of the original cells, and most preferablyall of the original cells, are absent from the engineered scaffold. Inembodiments, the remaining cells are cells that comprise vascular orneural structures. In preferred embodiments, some, most, or all of thecellular debris from the cells is absent from the engineered scaffold.Likewise, in embodiments, the tissue scaffold contains some or all ofthe neurons originally present in the tissue. However, in embodiments,the neurons are destroyed but the neural tubes in which the neuronsexisted remain intact.

In some embodiments, the engineered scaffold comprises cell debris fromcells originally (i.e., naturally) populating the scaffold. As discussedabove, in such embodiments, the cell debris can be removed using knownmeans. Alternatively, some or all of the cell debris may be left in andon the scaffold. In embodiments where cell debris is left on thescaffold, it can be later removed by the action of new cells seeded ontothe scaffold and/or during the process of seeding, infiltration, andgrowth of new cells. For example, where new cells are seeded onto ascaffold comprising cell debris, the action of the new cellsinfiltrating and growing, alone or in combination with a perfusion meansfor feeding and supporting the new cells, can result in removal of thecell debris.

The present invention provides engineered tissue scaffolds that comprisevascular structures that can function in providing nutrients and gasesto cells growing on and in the scaffolds. The use of non-thermal IRE tocreate the engineered scaffolds permits retention of these importantstructures, and thus provides for improved scaffolds for use in medical,veterinary, and research activities. The invention thus providesengineered scaffolds capable of having relatively large dimensions. Thatis, because re-seeded cells growing within the inventive scaffolds neednot be close (i.e., within 1 mm) to an external surface in order toobtain nutrients and gas, the engineered scaffolds may be thicker thanscaffolds previously known in the art. Engineered scaffolds may havethicknesses of any desirable range, the only limitation being theability to generate the appropriate electrical field to causedecellularization. However, such a limitation is not a significantphysical constraint, as placement of electrodes to affect IRE is easilyadjusted and manipulated according to the desires of the practitionersof the invention.

Engineered scaffolds of the invention can have thicknesses that approachor mimic the thicknesses of the tissues and organs from which they arederived. Exemplary thicknesses range from relatively thin 1 mm or less)to moderately thick (i.e., about 5 mm to 1 cm) to relatively thick(i.e., 5 cm or more, such as 10-20 cm or more).

Examples of providing engineered scaffolds from IRE of tissues duringactive perfusion according to methods of the invention are providedbelow. Ideally IRE performed ex vivo should be done as the tissue isperfused in a bioreactor. Perfusion of tissue in a bioreactor has beenpublished in the literature, and the parameters disclosed therein can begenerally applied within the present context. IRE is a special mode forcell ablation perfectly suitable to creating scaffolds because it killsthe cells in the targeted area while sparing major blood vessels,connective tissue, nerves, and the surrounding tissue. Typically, mildenzymes or chemicals (non-ionic detergents, zwitterionic detergents,chelating agents, enzymatic methods) can be used to facilitate removalof DNA fragments after decellularization (for IRE in vivo, the removalof cells can be accomplished by the body's natural system).

One approach to implementing IRE ex vivo with a bioreactor perfusionsystem includes: (a) attaching a freshly excised organ to a bioreactorperfusion system to maintain physiological environment or under othertemperature conditions to achieve a particular result; (b) insertingelectrodes into targeted area, such as within the vasculature of theorgan; (c) subjecting the organ to perfusion with saline or anotherappropriate perfusate; and (d) administering electrical pulses throughone or more electrode to administer reversible or irreversibleelectroporation through the vasculature. Once undesired cells areablated, the cellular debris can be removed using chemical (e.g.,non-ionic detergent) or physical techniques to remove cellularcontent/debris (especially if ex vivo). The scaffold can then be seededwith seed cells into the targeted/treated area. Additional perfusion ofthe organ can be performed to administer nutrients and/or growth mediato the seeded cells (demonstration of perfusion during IRE in Edd etal., 2006) and the bioreactor perfusion system can be maintained atoptimal conditions for cell growth (37° C.). Any one or more of thesemethod steps can be performed and in any order to achieve a desiredvolume of treated tissue. For example, to treat several areas of anorgan or to treat the entire organ, electroporation can be repeated overseveral smaller areas of the organ and intermittent with substantialresting periods where perfusion is allowed to flush cell debris from theorgan, or a substantial period of perfusion without IRE can be allowedto take place after IRE is performed. Likewise, if using plate or needletype electrodes, perfusion can be allowed to take place prior toplacement of or insertion of the electrodes, whereas with wire typeelectrodes placed within the vasculature, it may be desired to place theelectrodes appropriately then begin the active perfusion. Indeed, anyone or more these steps can be omitted, modified, rearranged with othersteps, or substituted for other steps as appropriate.

Example II—IRE During Active Perfusion

Young mixed breed pigs were sacrificed by way of barbiturate overdose.Livers were harvested and placed on ice within 15 minutes of death.Vascular anastomosis with the perfusion system was created by insertingLuer lock syringe connections into the portal vein, hepatic artery, andmajor hepatic vein, which were then secured with zip ties. The liverswere flushed with lactated Ringer's solution (LRS) to remove blood/clotsbefore placement on the perfusion system.

The VasoWave™ Perfusion System (Smart Perfusion, Denver, N.C.) was usedto perfuse the livers for 4 and 24 hours. This system produces acardioemulating pulse wave to generate physiological systolic anddiastolic pressures and flow rates within the organ. The system iscapable of controlling the oxygen content of the perfusate above andbelow physiological norms. A perfusate, consisting of modified LRS, wasdelivered to the portal vein and hepatic artery and recycled back intothe system through the hepatic vein. All livers were under activemachine perfusion within one hour post-mortem.

While under perfusion, the ECM 830 Square Wave BTX ElectroporationSystem (Harvard Apparatus, Cambridge, Mass.) was used to deliverlow-energy pulses to the liver tissue. Two metal plate electrodes, 2 cmin diameter, were attached to a pair of ratcheting vice grips (38 mm,Irwin Quick-Grips) using Velcro. High voltage wire was used to connectthe electrodes to the BTX unit. The electrodes were clamped gently tothe liver and the center-to-center distance between the electrodes wasmeasured. The voltage output on the BTX unit was adjusted such that theapproximate applied electric field was 1000 V/cm.

Ninety-nine individual 100-μs square pulses were administered atrepetition rates of 0.25, 0.5, 1.0 and 4.0 Hz. Repetition rates trialswere performed at random and repeated a minimum of three times. Shamcontrols were performed by placing the electrodes over the tissuewithout delivering any pulses. Two additional trials were performedusing needle electrodes placed on a 0.5 cm gap using avoltage-to-distance ratio of 1500 V/cm at rates of 1 Hz and 4 Hz. Theset up for this protocol is found in FIG. 5A. All N-TIRE treatments werecompleted within two hours post mortem. The surface lesion created ateach treatment site was measured at the end of the 24 hour perfusionperiod. FIGS. 5A-B are drawings of (FIG. 5A) placement of the electrodes(one of which is shown by reference number 50) on actively perfusedliver tissue 55 and (FIG. 5B) the resultant lesion 64 after treatmentwith 99, 100 μs, 1500V/cm pulses and 4 hours of perfusion, with theapproximate area of the electrode outlined by region 60.

Following N-TIRE treatment and machine perfusion, livers weredisconnected from the VasoWave™ system, sectioned to preserve lesions,and tissues were fixed by immersion in 10% neutral buffered formalinsolution. After fixation, tissues were trimmed and processed for routineparaffin embedding, then sectioned at 4 micrometers, and stained withhematoxylin-eosin (H&E) and trichrome stains. Tissue sections wereevaluated by a veterinary pathologist who had no knowledge of the N-TIREtreatment parameters.

Numerical modeling can be used to predict the electric fielddistribution, and thus provide insight into the N-TIRE treatment regionsin tissue. Edd, J. F. & Davalos, R. V. Mathematical modeling ofirreversible electroporation for treatment planning. Technology inCancer Research and Treatment 6, 275-286 (2007) (“Edd 2007”). This hasbeen chosen as the method to correlate lesion volume with an effectiveelectric field threshold for the lesions created in the liver. Themethods for predicting N-TIRE areas are similar to the ones described byEdd and Davalos. (Edd 2007). In order to understand the effectiveelectric field threshold to induce N-TIRE in the liver, finite elementsimulations were conducted using Comsol Multiphysics 3.5a (Comsol,Stockholm, Sweden). The numerical model was constructed using 2 cmdiameter plates, each 1 mm thick, placed above and below the tissue. Themodel was solved as prescribed by Garcia et al. (Garcia, P. et al.Intracranial nonthermal irreversible electroporation: in vivo analysis.J Membr Biol 236, 127-136 (2010)). The electric field distribution isgiven by solving the Laplace equation:

∇·(σ∇ϕ)=0

where σ is the electric conductivity of the tissue and φ is thepotential.

The electrical boundary condition along the tissue that is in contactwith the energized electrode is φ=V_(o). The electrical boundarycondition at the interface of the other electrode is φ=0. The boundarieswhere the analyzed domain is not in contact with an electrode aretreated as electrical insulation. The electrical boundary conditionalong the tissue that is in contact with the energized electrode isφ=V_(o). The electrical boundary condition at the interface of the otherelectrode is φ=0. The boundaries where the analyzed domain is not incontact with an electrode are treated as electrically insulative.

Conductivity changes due to electroporation and temperature have beenmodeled to calculate the dynamic conductivity according to the followingequation:

σ_(dynamic)(normE_dc)=σ₀[1+flc2hs(normE_dc−E_(delta), E_(range))] whereσ₀ is the baseline conductivity. flc2hs is a smoothed heavyside functionwith a continuous second derivative that ensures convergence of thenumerical solution. This function is defined in Comsol, and it changesfrom zero to one when normE_dc E_(delta)=0 over the range E_(range). Inthe function, normE_dc is the magnitude of the electric field, andE_(delta) is the magnitude of the electric field at which the transitionoccurs over the range, E_(range). In the simulations, the following wereused: E_(delta)=500V/cm and E_(range)=100 V/cm. The baseline tissueconductivity was of 0.286 S/m, and N-TIRE affected tissue was consideredto double as used by Sel et al., reaching a final conductivity of 0.572S/m. (See Boone, K., Barber, D. & Brown, B. Review—Imaging withelectricity: report of the European Concerted Action on ImpedanceTomography. J. Med. Eng. Technol. 21, 201-232 (1997); Sel, D., Lebar, A.M. & Miklavcic, D. Feasibility of employing model-based optimization ofpulse amplitude and electrode distance for effective tumorelectropermeabilization. IEEE Trans Biomed Eng 54, 773-781 (2007); Sel,D. et al. Sequential finite element model of tissueelectropermeabilization. IEEE Trans Biomed Eng 52, 816-827,doi:10.1109/TBME.2005.845212 (2005); and Payselj, N. et al. The courseof tissue permeabilization studied on a mathematical model of asubcutaneous tumor in small animals. IEEE Trans Biomed Eng 52, 1373-1381(2005)).

This numerical model was solved for the pulse parameters used on thelivers in order to obtain a simulation of the electric field to whichthe tissue was exposed. The N-TIRE electric field thresholds were thenfound by measuring lesion dimensions and determining the electric fieldvalue at this region in the model.

Surface lesions develop during perfusion within 30 minutes initiating oftreatment. The area of these on the liver surface created by plateelectrodes were larger than, but the same type as that from the needleelectrodes. In FIG. 5B, a 3.3 cm surface lesion produced from an appliedvoltage of 1500 V may be seen, taken 4 hours after treatment.Numerically modeled, this lesion size was produced within the region oftissue experiencing an electric field of 379±142 V/cm or greater. Theresults of the numerical model for this trial may be seen in FIGS. 6A-C.

The average applied voltage to distance ratio between the plates for thefrequency trials was 962 V/cm. Lesions from these trials developed over22 hours post-treatment, and were 2.5 cm in diameter on average (125%electrode diameter); with a minimum lesion of 2 cm occurring at 0.25 Hzand 936 V/cm, and maximum lesion of 3.2 cm occurring at 1.0 Hz and 950V/cm. Though not dramatically significant, the results suggest thatlesion sizes were on average greatest at 1 Hz and decreased as thefrequency increased or decreased. The lesions which developed aftertreatments applied at 0.25 and 4 Hz were statistically smaller (α=0.1)than those which developed for treatments applied at 1 Hz (FIGS. 7A-B).

Analysis of the treated tissue reveals a uniform treatment region thatextended cylindrically through the tissue. This resulted in calculatedtreated volumes between 1.97 cm³ and 6.37 cm³ for corresponding tissuethicknesses of 0.628 and 0.792 cm.

On histological examination from 24 hours post-treatment, the treatedregions exhibit cell death (FIG. 8B) compared to controls (FIG. 8A).More specifically, FIGS. 8A-B show the histological comparison ofuntreated liver tissue to areas which have undergone mild IRE treatmentsshowing preservation of connective tissue and blood vessels. Samplesstained with H&E from (FIG. 8A) untreated and (FIG. 8B) ninety nine, 100μs, 1000V/cm pulses using plate electrodes 24 hours of cardio emulationperfusion at 10×.

Hepatic acini in pigs are bordered by connective tissue, which containsblood vessels and biliary structures, and have a prominent cordarchitecture terminating in a hepatic venule. In areas adjacent toenergy delivery, hepatic cell cords were well preserved, with mildlyvacuolated hepatocytes (an expected finding at 24-hour ex vivo machineperfusion cycle). Sinusoidal structure in untreated areas is open,reflecting the flow of perfusate between hepatic artery/portal vein andhepatic vein. N-TIRE treatment disrupts hepatic cords and induces celldegeneration (FIG. 8B). Preservation of major acinar features, includingconnective tissue borders and blood vessels, is seen. In zones of N-TIREtreatment, cell cords were indistinct and membranes lining sinusoids arefragmented to varying degrees.

Pigs, like humans, have substantial septation of liver acini by thinbands of fibrous connective tissue that run between portal triads. Thismacrostructure had an effect on the distribution of lesions induced byelectroporation. Lesions are confined within structural acini in amanner that at the edges of the electroporation field, acini withlesions could border normal or nearly normal acini. Thus, the bands ofconnective tissue act as insulation for the electrical pulsing, animportant observation when considering procedures for treating focalliver lesions with electroporation or for evolving an intact connectivetissue/duct/vascular matrix for subsequent tissue engineering.

FIGS. 9A-C are micrographs showing (FIG. 9A) A section of untreatedliver after 24 hours of perfusion. Sections of the same liver treatedwith 90, 1500V/cm, 100 μs pulses at 4 Hz using needle electrodes after24 hours of perfusion at (FIG. 9B) 10× and (FIG. 9C) 20× magnification.

FIG. 9A shows a portion of untreated porcine liver with normalsinusoidal cell cords arrayed from portal tracts to central vein. Cellmorphology is well preserved. Some vascular congestion with red bloodcells is noted and there is also mild centrilobular biliary stasis.Mildly damaged porcine acini are observed in regions subjected to plateelectroporation (FIG. 9B). The center of the acinus shows disruption ofcord architecture and some cell degeneration and clumping. A highermagnification view of this area is shown in FIG. 9C, where cellularchanges are more readily appreciated. These treated regions display mildlesions consisting of hepatocytic cord disruption and cells delaminatingfrom cord basal laminae. Mild biliary stasis is noted (dark pigment).

Administration of N-TIRE treatment, either with needle electrodes orwith plate electrodes produced lesions in some hepatic acini that aredistinctive. The severity of lesions within individual acini ranges frommild to moderately severe. Mild lesions consisted of small clumps ofhepatocytes that detach from basal membranes. These cells show a loss oforganization of fine intracellular structure and clumping ofcytoplasm/organelles (FIGS. 9A-C).

Moderately severe lesions are readily discerned (FIGS. 10A-B). Cellsaffected by the N-TIRE procedure show varying degrees of cell swellingand karyolysis (FIG. 10B). Within individual acini, most cells areaffected. In some acini, frank nuclear pyknosis and cellulardegeneration is seen, with small clumps of hyperchromic cells unattachedfrom basal membranes. In some acini, centrilobular biliary stasis isnoted, with aggregation of bile pigments in distal sinusoidal spaces. Inall cases, as noted, bridging bands of connective tissue, with intactbile ducts and vascular structures are seen, even immediately borderingacini with significant N-TIRE-induced tissue damage.

This work reports the effect of non-thermal irreversible electroporationin an actively perfused organ for use in creating decellularized tissuescaffolds for organ transplantation. The results reported here werelocalized to volumes of tissue up to 6.37 cm³ for a single N-TIREtreatment. This can readily be expanded into much larger volumes byperforming multiple treatments with the goal of creating decellularizedstructures for partial and full liver transplants. After 24 hours ofperfusion, a quantity of cellular debris usually remained within thetissue construct. Removal of this debris is essential in minimizingimmune response of recipients and can be accomplished through longer andmore efficient perfusion protocols and/or using the body's ownmechanisms of perfusion to maximize the removal of cellularconstituents.

In addition to producing decellularized tissue scaffolds, these methodsprovide an ideal platform to study the effects of pulse parameters suchas pulse length, repetition rate, and field strength on whole organstructures. Additionally, since there is direct control over theelectrical properties of the perfusate, this could serve as a model forexamining the effects of N-TIRE on diseased or cancerous organs withunique electrical or physical properties. Methods of the invention canbe applied to treat portions of diseased tissue or organs to removeunwanted or diseased tissue, then re-seeding of the organ or tissue canbe performed. For example, a patient with liver disease could be treatedto address just the damaged regions of the liver through the vasculatureand allow the body to decellularize and reseed that section on its own.

The resulting scaffolds from N-TIRE plus perfusion maintain thevasculature necessary for perfusion into structures far beyond thenutrient diffusion limit that exists for non-vascularized structures.Since the temperature of the perfusate used can be as low as 4° C.,thermal aspects associated with Joule heating are negligible. Thisprovides an ideal platform in which to explore the effects on the cellsand tissue of electric fields in isolation from the effects of thermaldamage. Additionally, the low temperature of the organ compared to invivo applications may allow for the application of much higher voltagesto attain appropriate electric fields for decellularizing thickerstructures without inducing thermal damage. This is important since thethickness of a human liver can exceed 10 cm in some regions.

As shown and described herein, when planning to decellularize tissuesand organs undergoing active perfusion, the treatment region ofdecellularized tissue may be predicted through numerical modeling. Fromthe lesion sizes and numerical model used here, when decellularizing anentire organ for a transplantable scaffold, the protocol should exposeall of the tissue to an electric field of 379±142 V/cm. This will ensurecomplete cell death, allowing comprehensive reseeding of the scaffoldwith the desired cells, thus minimizing the effects of recipientrejection. It is noted that the threshold found here is slightly lowerthan ones in previous investigations, which may be a result of theunique pulse parameters used or an inherent increased sensitivity of thecells to the pulses when under perfusion.

Continuous active machine perfusion in the decellularization process mayalso be advantageous for recellularization. Once the decellularizationprocess is complete, it should be possible to reseed the scaffoldwithout risking damage attendant with removing the newly-createdscaffold from the perfusion system. Since the arterial and venoussupplies are individually addressable, multiple cell types can bedelivered simultaneously to different regions of the organ. Similarly,retrograde perfusion through the biliary system may be the ideal pathwayin which to deliver hepatocytes for the reseeding process.

Lesions seen microscopically are clearly indicative of a mechanism andmorphology for cellular stripping using electroporation. It is veryinteresting that even at 24 hours, when using the electroporationparameters described here, there is only a modest loss of acinararchitecture. More stringent conditions of energy delivery could likelyalter this, but this might induce damage to important connective tissueand vascular structures. Addition of adjuvant cytotoxic agents, enzymes,and detergents in the perfusion fluid also might modulate the severityand temporal nature of cell stripping. Logically, it is much better tobuild on mild conditions, preserving important architecture for tissueengineering purposes, than to rapidly obliterate cells and stroma. Theability to manage the period of perfusion and conditions of perfusionwith the cardioemulation system has clear advantages for this gradual,evolutionary approach to decellularization and eventualrecellularization of liver.

Example III—Vasculature Administered IRE with Active Perfusion

A normal kidney was procured, through standard and approved means, froma pig after death. When obtained, the renal artery and vein of thekidney were isolated and connected with fittings to allow anastomosis toa cardiovascular emulation system (CVES) (VasoWave 2.3™, Smart PerfusionLLC, Denver, N.C.). The organ was connected to the CVES and the kidneywas flushed with 1.5 liters of Krebs-Hensleit/Glutathione physiologicsolution over a period of 5 minutes.

The kidney was then anastomosed on the arterial and vascular connectorsto the CVES and perfusion was started (arterial systolic pressure:110 mmHg, diastolic pressure 60 mm Hg, with a physiologic pulse traindelivered at 60 beats per minute). Perfusion was performed at 25° C. Therenal vein was left disconnected but the end of the tubing was elevatedto generate a low backpressure (this approximated 1 mm Hg). Perfusionwas stabilized over a 15 minute interval. The Krebs solutionconductivity was measured at 0.72 S/m.

As shown in FIG. 11, customized energy application electrodes can befabricated for a particular application. In this example, anelectroporation device 70 was created by piercing a small section offlexible tubing 72 near its center point, inserting an insulated wireelectrode 78 with an exposed tip 78A (e.g., some portion of bare wire orenamel coated wire with an exposed tip) through the hole and sealing thesite with adhesive. The enamel on ends of the wire was removed to createelectrical connections within the tubing and externally while providingan insulating coating around the majority of the wire for safety. Inaddition, shrink wrap tubing was applied along the length of the tubingfor further electrical insulation. Luer lock connections 74, 76 werethen inserted into the ends of the tubing to facilitate connection tothe perfusion system. This electrode configuration presented less than 1ohm of resistance between the pulse generation system and the perfusedfluid. As shown in FIG. 11, a small diameter wire is situated inside thetubing and is accessible from the outside, which allows for pulses to bedelivered simultaneous with perfusion.

FIG. 12 is a drawing showing a kidney 80 simultaneously attached to theprototype electrodes 70 and perfusion system by way of the renal veinand artery. One electrode was placed in-line between the arterial supplyfrom the CVES and the kidney vascular connector. The venous electrodewas connected to the renal vein vascular connector on one end, while theother end of the electrode tubing was propped up with a syringe tocreate the backpressure. This also prevented the electrical current fromfinding a path of least resistance through the perfusate backwardsthrough the CVES or sending a partial current through the system and thekidney.

The resistance and capacitance of the vascular network was measured withan LCR meter. At low frequencies (100 Hz) the resistance and capacitancevalues measured were 372.6 k Ohms and 0.248 nano-Farads, respectively.This yields an RC time constant of 92.4 micro-seconds and a completedecay time (5*RC) of approximately 462 micro-seconds.

As demonstrated in FIG. 13, which provides impedance measurements fromthe kidney prior to pulsing, the organ presented a significantelectrical resistance and capacitance. The trend observed between 100and 10,000 Hz (FIG. 13) indicates that for square wave pulses which havea large direct current DC component, the RC time constant should belarger. A single 50 micro-second pulse was delivered through thevasculature at voltages of 100, 500, 750, 1000, 1500, and 2000 V using aBTX pulse generator (Harvard Apparatus). The current delivered and thedecay time of the pulse was recorded. In all cases, the decay time wasless than predicted.

The resultant waveform is shown in FIG. 14. More particularly, FIG. 14provides the resultant waveform from a 50 microsecond pulse withamplitude of 1000V. Decay of the pulse is characteristic of a tissuewith both resistive and capacitive components. A representative pulsevoltage and current plots can be seen in FIG. 14. The decay timedecreased significantly between 100 V and 500 V and remained relativelyconstant at voltages between 500 and 2000 V. In all cases, the deliveredcurrent was (23-53%) greater than expected based on calculations.

FIG. 15 is a graph showing the maximum current delivered and decay timefor pulses delivered with amplitudes between 100 and 2000 V. Trendsindicate that for pulses of 500 V and above, the resistance of thetissue has decreased due to electroporation. The organ was thensubjected to 200 pulses at 1000 V, with a repetition rate of one pulseevery second.

TTC stain (2% in Krebs solution) was administered by perfusion for 15minutes after pulsing was completed and the organ remained on theperfusion system for another 30 minutes. The TTC stain is used todelineate viable and non-viable tissue, via the formation of a coloredreaction product (a red formazan) through the activity of tissuedehydrogenases. Viable tissue, capable of oxidative respiration, isshown at 80; devitalized or ischemic tissue is pale in comparison, shownat 84. As shown in FIG. 16, a kidney section 30 minutes after pulsingshows areas indicative of live tissue, region 80, and areas indicativeof regions ablated by the IRE pulses, region 84. The sectioned organ wasplaced in formalin for fixation and histology. It is obvious from thisfigure that a large volume of the kidney underwent irreversibleelectroporation. Blood clots in the vasculature may have prevented theentire organ from undergoing electroporation. This issue can be resolvedby flushing the vasculature of the organ immediately after surgicalresection.

FIGS. 17-19 are drawings showing that electroporation devices andsystems of the invention can be disposed in communication with bloodvessels and conductance structures of organs, such as the liver. FIG. 17shows device 70 (with electrode 78 comprising an exposed tip 78A) placedin hepatic artery 56 of liver 55. For reference, portal vein 57 and bileduct 58 are also shown. FIG. 18 is a drawing depicting oneelectroporation device 70 disposed in portal vein 57 of liver 55. FIG.19 is a drawing depicting one device with electrode placed into the bileduct 58 of a liver.

The vasculature and microvasculature of an organ can be used to deliverbrief but intense electrical pulses to bulk tissue resulting innon-thermal cell death while maintaining the structure and function ofthe underlying extracellular matrix. Histological staining will be usedto evaluate the overall health of the tissue (H&E), damage and removalof endothelial cells (vWF), and the structure of the extracellularmatrix (trichrome) and the resultant decellularization of thesepreliminary experiments. The 4 hour total perfusion protocol can be usedas a baseline for decellularization protocols and has extensions outsideof tissue engineering, such as to treat solid tumors which are embeddeddeep inside vascularized organs.

Once engineered scaffolds are prepared, the scaffolds can be furtherengineered to regenerate within a living body or engineered into tissuesand organs acceptable for transplantation into a living body. Methods ofmaking engineered tissues can comprise: seeding an engineered scaffoldaccording to the invention with a cell of interest, and exposing theseeded scaffold to conditions whereby the seeded cells can infiltratethe scaffold matrix and grow. Seeding of the scaffold can be by anytechnique known in the art. Likewise, exposing the seeded scaffold toconditions whereby the cells can infiltrate the scaffold and grow can beany technique known in the art for achieving the result. For example, itcan comprise incubating the seeded scaffold in vitro in a commercialincubator at about 37° C. in commercial growth media, which can besupplemented with appropriate growth factors, antibiotics, etc., ifdesired. Those of skill in the art are fully capable of selectingappropriate seeding and proliferation techniques and parameters withouta detailed description herein. In other words, with respect to seedingand growth of cells, the scaffolds of the present invention generallybehave in a similar manner to other natural scaffolds known in the art.Although the present scaffolds have beneficial properties not possessedby other scaffolds, these properties do not significantly affect seedingand growth of cells.

Engineered tissues have been developed as replacements for injured,diseased, or otherwise defective tissues. An important goal in the fieldof tissue engineering is to develop tissues for medical/therapeutic usein human health. In view of the difficulty and ethical issuessurrounding use of human tissues as a source of scaffolds, tissues fromlarge animals are typically used for the source material for naturalscaffolds. The xenotypic scaffolds are then seeded with human cells foruse in vivo in humans. While the presently disclosed engineered tissuesare not limited to human tissues based on animal scaffolds, it isenvisioned that a primary configuration of the engineered tissues willhave that make-up. Thus, in embodiments, the engineered tissues of theinvention are tissues comprising human cells on and within a scaffoldderived from an animal tissue other than human tissue.

For certain in vivo uses, animal tissue is subjected in vivo tonon-thermal IRE, and the treated tissue cleared of cell debris by thehost animal's body. Thus, in certain in vivo embodiments, no secondarycell debris removal step is required, as the host animal's body itselfis capable of such removal (this concept applies to in vivo creation ofscaffolds in humans as well). The treated tissue is then seeded in vivo,for example with human cells, and the seeded cells allowed to infiltratethe scaffold and grow. Upon suitable infiltration and growth, theregenerated tissue is removed, preferably cleaned of possiblecontaminating host cells, and implanted into a recipient animal, forexample a human. In such a situation, it is preferred that the hostanimal is one that has an impaired immune system that is incapable orpoorly capable of recognizing the seeded cells as foreign cells. Forexample, a genetically modified animal having an impaired immune systemcan be used as the host animal. Alternatively, for example, the hostanimal can be given immune-suppressing agents to reduce or eliminate theanimal's immune response to the seeded cells.

The recipient or host animal can be any animal, including humans,companion animals (i.e., a pet, such as a dog or cat), farm animals(e.g., a bovine, porcine, ovine), or sporting animals (e.g., a horse).The invention thus has applicability to both human and veterinarianhealth care and research fields.

Whether in vivo or in vitro or ex vivo, the choice of cells to be seededwill be left to the practitioner. Many cell types can be obtained, andthose of skill in the tissue engineering field can easily determinewhich type of cell to use for seeding of tissues. For example, one mayelect to use fibroblasts, chondrocytes, or hepatocytes. In embodiments,embryonic or adult stem cells, such as mesenchymal stem cells, are usedto seed the scaffolds. The source of seeded cells is not particularlylimited. Thus, the seeded cells may be autologous, syngenic or isogenic,allogenic, or xenogenic. Because a feature of the present invention isthe production of scaffolds and tissues that have reduced immunogenicity(as compared to scaffolds and tissues currently known in the art), it ispreferred that the seeded cells be autologous (with relation to therecipient of the engineered tissue). In certain embodiments, it ispreferred that the seeded cells be stem cells or other cells that areable to differentiate into the proper cell type for the tissue ofinterest.

Alternatively or additionally, the in vivo method of creating a scaffoldand the in vivo method of creating an engineered tissue can includetreating tissue near the non-thermal IRE treated cells with reversibleelectroporation. As part of the reversible electroporation, one or moregenetic elements, proteins, or other substances (e.g., drugs) may beinserted into the treated cells. The genetic elements can include codingregions or other information that, when expressed, reduces interactionof the cells with the seeded cells, or otherwise producesanti-inflammatory or other anti-immunity substances. Short-termexpression of such genetic elements can enhance the ability to growengineered tissues in vivo without damage or rejection. Proteins andother substances can have an effect directly, either within thereversibly electroporated cells or as products released from the cellsafter electroporation.

Certain embodiments of the invention relate to use of human scaffoldsfor use in preparation of engineered human tissues. As with otherengineered tissues, such engineered tissues can be created in vitro, invivo, or partially in vitro and partially in vivo. For example, tissuedonors may have part or all of a tissue subjected to non-thermal IRE toproduce a scaffold for tissue engineering for implantation of arecipient's cells, then growth of those cells. Upon infiltration andgrowth of the implanted cells, the tissue can be removed and implantedinto the recipient in need of it. Of course, due to ethical concerns,the donor tissue should be tissue that is not critical for the life andhealth of the donor. For example, the tissue can be a portion of aliver. The engineered tissue, upon removal from the host and implantedin the recipient, can regenerate an entire functional liver, while theremaining portion of the host's liver can regenerate the portionremoved.

Up to this point, the invention has been described in terms ofengineered tissue scaffolds, engineered tissues, and methods of makingthem. It is important to note that the invention includes engineeredorgans and methods of making them as well. It is generally regarded thatorgans are defined portions of a multicellular animal that perform adiscrete function or set of functions for the animal. It is furthergenerally regarded that organs are made from tissues, and can be madefrom multiple types of tissues. Because the present invention isgenerally applicable to both tissues and organs, and the distinctionbetween the two is not critical for understanding or practice of theinvention, the terms “tissue” and “organ” are used hereininterchangeably and with no intent to differentiate between the two.

Among the many concepts encompassed by the present invention, mentionmay be made of several exemplary concepts relating to engineeredtissues. For example, in creating engineered organs, the initial organcan be completely removed of cells using irreversible electroporationprior to reseeding (this is especially relevant for organs having atleast one dimension that is less than 1 mm); the organ can beirreversibly electroporated in sections and reseeded to allow the humancells to infiltrate small sections at a time; the organ can beirreversibly electroporated in incremental slices introducing the cellsin stages, so that no human viable cells are in contact with the viableanimal cells they are replacing; the organ can be irreversiblyelectroporated entirely or in sections and the human cells can beinjected into targeted locations in the organ; the entire organ can beirreversibly electroporated to kill the animal cells, then human cellscan be replanted on top of the organ to infiltrate the scaffold andreplace the other cells (as the animal cells die, the human cells willfill in and substitute, thereby creating a new organ.)

Having provided isolated engineered tissues and organs, it is possibleto provide methods of using them. The invention contemplates use of theengineered tissues in both in vitro and in vivo settings. Thus, theinvention provides for use of the engineered tissues for researchpurposes and for therapeutic or medical/veterinary purposes. In researchsettings, an enormous number of practical applications exist for thetechnology. One example of such applications is use of the engineeredtissues in an ex vivo cancer model, such as one to test theeffectiveness of various ablation techniques (including, for example,radiation treatment, chemotherapy treatment, or a combination) in a lab,thus avoiding use of ill patients to optimize a treatment method. Forexample, one can attach a recently removed liver (e.g., pig liver) to abioreactor or scaffold and treat the liver to ablate tissue. Inaddition, due to the absence of significant numbers of immune cells,tumors can be grown in the removed organs either by spontaneous means(carcinogens) or the introduction of tumorigenic cell lines into thetissue. These tumors may then be treated to improve understanding andpromote optimization of a therapeutic technique in a morephysiologically relevant, orthotopic setting. Another example of an invivo use is for tissue engineering.

The engineered tissues of the present invention have use in vivo. Amongthe various uses, mention can be made of methods of in vivo treatment ofsubjects (used interchangeably herein with “patients”, and meant toencompass both human and animals). In general, for certain embodiments,methods of treating subjects comprise implanting an engineered tissueaccording to the invention into or on the surface of a subject, whereimplanting of the tissue results in a detectable change in the subject.The detectable change can be any change that can be detected using thenatural senses or using man-made devices. While any type of treatment isenvisioned by the present invention (e.g., therapeutic treatment of adisease or disorder, cosmetic treatment of skin blemishes, etc.), inmany embodiments, the treatment will be therapeutic treatment of adisease, disorder, or other affliction of a subject. As such, adetectable change may be detection of a change, preferably animprovement, in at least one clinical symptom of a disease or disorderaffecting the subject. Exemplary in vivo therapeutic methods includeregeneration of organs after treatment for a tumor, preparation of asurgical site for implantation of a medical device, skin grafting, andreplacement of part or all of a tissue or organ, such as one damaged ordestroyed by a disease or disorder (e.g., the liver). Exemplary organsor tissues include: heart, lung, liver, kidney, urinary bladder, spleen,pancreas, prostate, ovary, brain, ear, eye, or skin. In view of the factthat a subject may be a human or animal, the present invention has bothmedical and veterinary applications.

For example, the method of treating may be a method of regenerating adiseased or dysfunctional tissue in a subject. The method can compriseexposing a tissue to non-thermal IRE to kill cells of the treated tissueand create a tissue scaffold. The method can further comprise seedingthe tissue scaffold with cells from outside of the subject, and allowingthe seeded cells to proliferate in and on the tissue scaffold.Proliferation produces a regenerated tissue that contains healthy andfunctional cells. Such a method does not require removal of the tissuescaffold from the subject. Rather, the scaffold is created from theoriginal tissue, then is re-seeded with healthy, functional cells. Theentire process of scaffold creation, engineered tissue creation, andtreatment of the subject is performed in vivo, with the possibleexception of expansion of the cells to be seeded, which can beperformed, if desired, in vitro.

In yet another exemplary embodiment, a tissue scaffold is created usingnon-thermal IRE to ablate a tissue in a donor animal. The treated tissueis allowed to remain in the donor's body to allow the body to clearcellular debris from the tissue scaffold. After an adequate amount oftime, the treated tissue is removed from the donor's body and implantedinto the recipient's body. The transplanted scaffold is not reseededwith external cells. Rather, the scaffold is naturally reseeded by therecipient's body to produce a functional tissue.

In yet another embodiment of the invention, the wire electrodes may beused to facilitate pulsed or continuous electric fields to inducereversible electroporation or thermal damage to a targeted region,either in vivo or ex vivo. Where it was shown in this example thatirreversible electroporation was possible to a majority of the organundergoing active perfusion, it has been proven that a tissue/organ'snative vasculature serves as an adequate electrical conduit for deliveryof the electric pulses to the tissue. Where reversible electroporationis a phenomenon that occurs at lower energy pulse parameters thanirreversible electroporation, it is clear that reversibleelectroporation through the vasculature is also possible. This techniquemay be very useful when the practitioner desires not to ablate thetargeted region, but introduce therapeutic macromolecules, such as genesor drugs, to the targeted region. The macromolecule used and desiredtherapeutic effect is left up to the practitioner. Furthermore,radiofrequency ablation is a commonly used thermal focal ablationtechnique which uses continuous alternating electric fields to heattissue, whose utility in medicine may be enhanced and invasivenessreduced by incorporating the vascular electrode techniques described inthis invention.

The present invention eliminates some of the major problems currentlyencountered with transplants. The methods described herein reduce therisk of rejection (as compared to traditional organ transplants) becausethe only cells remaining from the donor organ, if any, are cellsinvolved in forming blood vessels and nerves. Yet at the same time,vascular, neural, and glandular structures are maintained. The presentinvention provides a relatively rapid, effective, and straightforwardway to produce engineered tissues having substantially natural structureand function, and having reduced immunogenicity. As such, the engineeredtissues of the present invention are highly suitable for therapeutic andcosmetic use, while having a relatively low probability of rejection. Inembodiments where human organs are used as the source of the scaffold(e.g., from live organ donors or cadavers), the risk of rejection isvery small.

In summary, the inventors have demonstrated a novel process, usingnewly-fabricated tools (electrodes and perfusion systems), that can beused for highly selective ablation of unwanted soft tissue, includingcells, tissues and organs. Unique embodiments include application ofpulsed electrical energy in fluids contained within tubing or vascularbeds, control of perfusion fluid content and flow parameters, schemes ofpulsed energy delivery, and use of other manipulations to confine anddefine therapeutic effects. It has further been demonstrated thatcellular removal from intact tissues is possible and that this may beuseful for creation of novel tissue matrices for a variety of uses. Theresults presented here are based on experiments conducted ex-vivo.However, the perfused fluid was similar in composition and conductivityto blood. This indicates that these experimental results are indicativeof the responses which will be seen in-vivo.

The methods of energy delivery described in this specification, e.g.,directly through the vasculature of the organ, can also be used toinduce other therapeutic responses. Sub-lethal electric pulses(reversible electroporation) can be used to introduce genes or drugsinto a specific organ or region of an organ to treat localized diseases.Similarly, radiofrequency ablation techniques could use the vasculatureto deliver radiofrequency energy to destroy diseased tissue or tumorsthrough acute hyperthermia. These modalities could be enhanced bydelivering physiologically acceptable fluids (by way of co-perfusion)with different electrical properties to enhance these effects.

Because this energy is applied through the vasculature, large, yetcontrollable treatment volumes can be achieved. The overall structure ofthe organs is not disturbed because the energy is not being delivered byneedle electrodes and organ puncture is not necessary. In addition, aspredicted theoretically and validated experimentally, the deliveredenergy is being dissipated directly across the vascular or capillary bedrather than across bulk tissue. Typical treatments using needle or plateelectrodes use similar voltages, deliver currents in excess of 1 Amp,and affect small volumes. In contrast, delivery of energy using vascularnetwork of kidney results in currents on the order of 50 mA (200 timesless power) while treating significantly larger volumes.

Example IV—Measuring Vascular Capability to Conduct Electric Current

Rationale: Accurate measurement of vasculature resistance to electricalcurrent can play an important role in the development of accurate modelsand treatment protocols.

Exemplary Design: Sixteen porcine livers are harvested from mixed breedyoung pigs within two minutes of euthanasia induced via overdose ofbarbiturates. These tissues are immediately flushed with University ofWisconsin (UW) solution at 8° C. and placed on ice. Vascular anastomosiswith a cardioemulation perfusion system (VasoWave™ 2.0, Smart Perfusion,Denver, N.C.) can be achieved by inserting Luer lock connectors into theportal vein (PV), hepatic artery (HA), and major hepatic vein (MHW)within 15 minutes of euthanasia. Access to the biliary system can beachieved by attaching a similar connection to the common bile duct(CBD). The livers can be perfused for one hour prior to experimentationto guarantee homogeneous distribution of the perfused fluid (perfusate)and complete removal of blood cells and other plasma constituents. Thecomplex impedance (Z) of the vasculature can be measured by applyingsmall sine-wave voltage signals with frequencies oscillating between 3and 25 kHz. The voltage drop across the driving electrodes and currentthrough a known resistor in the current path can be measured. Thecomplex impedance between the following pairs can be calculated throughOhm's Law (Z=V/I); 1) PV-HA 2) PV-MHV 3) HA-MHV 4) PV-CBD 5) HA-CBD 6)MHV-CBD.

Overall Summary and Significance: The results from these experiments canprovide the electrical characteristics of the vasculature system and theability of each constituent to deliver charge. Impedance between theportal vein and hepatic artery is expected to be the least significantsince these pathways merge at the lobule level. Impedance between theportal vein—major hepatic vein and hepatic artery major hepatic veinpairs is expected to be greater since the microvasculature whichconnects these structures at the lobule level should provide significantresistances individually. The impedance between each of the vasculaturetracts and the common bile duct is expected to be the greatest sincethere should be no direct fluid path between these systems.

The present invention has been described with reference to particularembodiments having various features. It will be apparent to thoseskilled in the art that various modifications and variations can be madein the practice of the present invention without departing from thescope or spirit of the invention. One skilled in the art will recognizethat these features may be used singularly or in any combination basedon the requirements and specifications of a given application or design.Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention. Where a range of values is provided in this specification,each value between the upper and lower limits of that range is alsospecifically disclosed. The upper and lower limits of these smallerranges may independently be included or excluded in the range as well.As used in this specification, the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a pulse” includes a plurality of suchpulses and reference to “the sample” includes reference to one or moresamples and equivalents thereof known to those skilled in the art. It isintended that the specification and examples be considered as exemplaryin nature and that variations that do not depart from the essence of theinvention are intended to be within the scope of the invention. Further,the references cited in this disclosure are incorporated by referenceherein in their entireties.

1. (canceled)
 2. A method of ablating cells from tissue or an organcomprising: placing one or more electrode in, on, or near an organ ortissue; mechanically perfusing the tissue or organ with a perfusate; andadministering an electrical field into the tissue or organ for asufficient time and at sufficient power to cause electroporation oftarget cells.
 3. The method of claim 2, which is a therapy selected fromelectrochemotherapy (ECT), electrogenetherapy (EGT), nanosecond pulsedelectric fields (nsPEF), High-frequency Irreversible Electroporation(H-FIRE), radio frequency ablation, or acute hyperthermia.
 4. The methodof claim 2 further comprising administering an energy into thevasculature for a sufficient time and at sufficient power to cause deathof target cells.
 5. (canceled)
 6. The method of claim 2, wherein a firstelectrode is inserted into a blood vessel of the organ and a secondelectrode is inserted into another blood vessel of the organ andelectroporation is administered between the electrodes through thevasculature of the organ.
 7. The method of claim 2, wherein a firstelectrode is inserted into a blood vessel of the organ and a secondelectrode is inserted into a fluid duct of the organ and electroporationis administered between the electrodes through the vasculature of theorgan.
 8. (canceled)
 9. The method of claim 2, wherein a first electrodeis inserted into a blood vessel of the organ and a second externalgrounding pad, plate electrode, or conductive gel external to the organis used as a second electrode and electroporation is administeredbetween the electrodes through the vasculature of the organ.
 10. Themethod of claim 2, performed in a living animal or organ undermechanical perfusion wherein electric pulses are administered to inducean electrical field through the vasculature for a sufficient time and atsufficient power to cause electroporation of target cells to facilitatethe introduction of therapeutic gene constructs to treat either adisease occurring within the targeted region or a systemic disease. 11.(canceled)
 12. The method of claim 10, performed in a living animal ororgan under mechanical perfusion wherein electric pulses areadministered to induce an electrical field through the vasculature for asufficient time and at sufficient power to cause electroporation oftarget cells to facilitate the introduction of therapeuticmacromolecules to treat a disease, either within the targeted region ora systemic disease.
 13. The method of claim 10, performed in a livinganimal or organ under mechanical perfusion wherein administration ofalternating electric fields through the vasculature produces thermalablation of a targeted region or entirety of an organ.
 14. The method ofclaim 2, wherein the electroporation comprises non-thermal irreversibleelectroporation of target cells.
 15. The method of claim 2, furthercomprising removing cellular debris from the tissue or organ bymechanical perfusion, physiological perfusion, or physical, chemical, orenzymatic techniques, or any combination thereof.
 16. The method ofclaim 2, further comprising monitoring through electrical measurementsto detect and monitor electroporation.
 17. A tissue scaffold formed fromablation of target cells from a natural tissue source by administeringirreversible electroporation to the target cells during perfusion of thetissue.
 18. The scaffold of claim 17, wherein the electroporation isadministered through vasculature of the tissue.
 19. The scaffold ofclaim 17 comprising an extracellular matrix and vascular structure of anatural tissue source.
 20. The scaffold of claim 17, wherein the tissuescaffold has a thickness in at least one dimension of about 1-10 cm. 21.An engineered tissue formed from ablation of target cells from a naturaltissue source by administering irreversible electroporation to thetarget cells during perfusion of the tissue to obtain a tissue scaffold,and reseeding the scaffold with living cells under conditions thatpermit growth of the living cells on or in the scaffold.
 22. (canceled)23. The engineered tissue scaffold of claim 21, wherein the tissuescaffold is from an animal and the living cells are from a human. 24.The engineered tissue scaffold of claim 21, wherein the tissue scaffoldcomprises an extracellular matrix and vascular structure of a naturaltissue source.
 25. (canceled)
 26. The engineered tissue scaffold ofclaim 21, which is a heart, a lung, a liver, a kidney, a pancreas, aspleen, a gastrointestinal tract, a urinary bladder, a prostate, anovary, a brain, an ear, an eye, or skin, or a portion thereof. 27-28.(canceled)